Atlanta United Venue Analysis: Bobby Dodd Stadium vs Mercedes Benz Stadium vs Opponents Stadia

Josh over at Dirty South Soccer wrote a really nice piece on some of the observable differences between Atlanta United playing at Bobby Dodd and Mercedes Benz. Click here to check that out. I’m not as eloquent or as wise as him, nor as versed in soccer tactics, but I wanted to just drop some data / graphs in here that I’d been tweeting about in recent weeks to add to this comparison.

First up, here’s a table I keep to track some of the Atlanta United tidiness stats.

VenueTidinessCompare

Takeaway1: Atlanta are tidier on the ball at home, and more tidy on the ball at the Benz compared to Bobby Dodd. This shows up in the own-half passes per giveaways and own-half passing % metrics.

Takeaway2: Atlanta are suppressing opponents’ shots (and shots on target) at home, and most impressively at the Benz. The result is improved expected goals against figures as well as improved goals conceded figures.

Tweets that support this:

Next up, the pressing stats for Bobby Dodd, Mercedes Benz, and away matches:VenuePressingCompare

 

Takeaway1: Interestingly, while Atlanta United pressed more furiously and to greater effect at Bobby Dodd than on the road, the pressing numbers come down quite a bit at MBS – could be schedule congestion and fitness conservation – could be larger pitch makes it harder to press opponents into mistakes.

Takeaway 2: ATL Goals and Expected goals have trended up furiously at MBS compared to Bobby Dodd, both being higher than the average away matches output. Expected goal data comes from AmericanSoccerAnalysis.com as always.

 

Game by Game Pressing/Tidiness Game Stats (I hadn’t posted these here since the FCD match.

Finally, I wrote something about the inevitable sales of Atlanta United players and how this works out with the current MLS rules.

https://www.dirtysouthsoccer.com/atlanta-united-fc/2017/10/19/16465762/mls-transfer-rules-regulations-fees-percentages

God speed to everyone in the postseason.

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Updated table math and squad rotation and what’s left to play for

I wrote a piece for DirtySouthSoccer, which you can find here, where I update us all on the PACE standings as of Monday 9-25-17. Then I ponder some difficult questions around whether one can rotate the squad when there’s still so much left to play for. #4 comes with homefield advantage in the play-in round, #2 comes with a first round bye. Atlanta are favored to achieve both of these, but the Almiron injury…

On MLS Home Advantage and Playoff Structures

Home field advantage is a real thing in sports. And it impacts soccer more than any other major sport. Freakonomics argues that home field advantage is primarily driven by refereeing decisions as the raucous crowds have a conscious or subconscious impact on the referee when he goes to make difficult decisions. In soccer where the referee has greater latitude to make highly judgmental decisions that significantly impact the game, homefield advantage is felt the heaviest:

Home Field Advantage - Global Soccer

More interestingly, homefield advantage is greater in MLS than in the 5 major European leagues. In the major European leagues, home sides generally average 1.6+ ppg, but in MLS it is 1.8 ppg at home. This is a significant difference. Some have argued that the difficult travel times (unique to the larger US geography) and coach class commercial flights have a big impact here, but personally, I think it’s more likely that a similar homefield advantage exists in America as it does overseas (i.e. one that is primarily determined by important, judgmental referee decisions per Freakonomics), but that the parity of the league amplifies this effect. After all, if there is a very little difference between two teams facing one another on the field, any inherent advantage to the home side will show through more often. And this happens in MLS. And of course, MLS by design is a league of great parity relative to the European leagues. There’s a Salary Cap and some other interesting roster budget mechanisms that I’ve discussed before, several times. A league designed to be competitively even (like some other popular US-based professional leagues) should suffer more from the impact of unconsciously biased referee decisions. Perhaps this is why they are adopting V.A.R. ahead of the rest of the world. A post for another day.

But, here’s what I wanted to talk about: the Playoffs.

This week Sam Stejskal at FourFourTwo reported that MLS is considering an overhaul to the playoffs formatting due to scheduling issues where the FIFA international break slows down the “momentum” of the playoffs between the conference semi-final and final rounds. Currently those rounds are home and home double-legged affairs with away goals being the tiebreaker if aggregate scorelines are tied after 180 minutes plus stoppage. The reported proposal would swap out these double leg series for single elimination games hosted by the higher seeds. Stejskal mentions that the lower seeded team has won 8 of the 12 conference championship series since the current structure was introduced (this seems like a perfectly reasonable outcome over a sample as small as this if you buy that home and homes are mostly fair to both teams). Also posted at FourFourTwo acutally… while I was drafting this paragraph, is this piece by Steve Davis, who mentions that 11 out of 12 single elimination play-in games have gone to the home sides!

It is my opinion that switching to fully single elimination games hosted by the higher seeds would be a mistake because of the significant home field advantage in MLS, which is due to the significant level of parity in MLS (something the league purposefully designed). With teams averaging 1.8 points per game at home during the regular season and less than a point per game on the road during the regular season, these series would become largely “no contests” when that’s not what playoffs are supposed to be (my gut is that they would mirror the 11/12 play-in games going to the home team). Consider how few teams in MLS actually average more than 1.5 points per game (a favorable average) when playing away from home. Below is the full inventory of said teams over the past 5 years:

Home Field Advantage - Global Soccer 3

Also consider, how this stacks up to more traditional “Big 5 European Leagues” with traditionally less parity, in terms of percent of the league that averages 1.5+ ppg when playing away from home:

Home Field Advantage - Global Soccer 2

If no teams in your league can average a positive result when playing away, then why would you even hold a postseason in which every single round is laced with the most significant home field advantage observable in sports? It doesn’t make sense to me. Many out there want the team with the better record to be rewarded with an advantage in the playoffs. I understand this sentiment. After all, while playoffs are an exciting way to determine a league champion, the regular season should “matter” – especially in a sport like soccer, where the best leagues in the world determine their champion via a regular season table format. But my answer to these complaints is that first and foremost, the 2 best teams in each conference are absolutely rewarded something valuable, a bye – well earned rest, and the right not to be challenged by the 5th or 6th best teams in the conference. The third and fourth best teams are offered the significant homefield advantage vs the 6th and 5th best teams in the play-in rounds. But once we whittle the playoffs down to the top 4 teams in each conference, are we sure we want to try to reward incrementally different advantages to each of those 4 teams? In a league of parity and where the schedules aren’t balanced and New York Red Bulls and New York City FC have to play each other 3 times a year while Atlanta gets to face DCU (let’s not talk about it), if we were to award the 2nd best team a significant advantage over the 3rd place team in the East, would that even be fair? How certain would we be that the 2nd place team really earned this advantage? And as a reminder, the advantage given to the 2nd place team in this case would be massive based on the numbers mentioned above this post. From 2012-2016 in MLS, teams equivalent to the #4 seed in each conference average 1 point per game on the road against the league as a whole (including the basement dwellers of each conference). In short, it’s stacking the deck too much to let a team averaging 2.3 ppg at home (average top seed home record) host a team averaging 1 ppg on the road (avg #4 seed away record) and have this be the meat of your postseason (conference semi-finals and conference finals).

In summary, MLS created a league based mainly on the traditional American socialist-oligopoly high-parity sports model (NFL, NBA), and not on the free-market model (MLB, EPL, etc). In doing so, the league needs to accept that it values parity, and that having chosen a playoff-determines-champion model, the league needs to accept that it mainly* values the “what-happens-in-the-postseason-is-what-matters” concept. Those two ideas work decently well together, and the main benefit is that the playoffs are interesting because in most postseason games, they offer a visceral and tangible moment to distinguish two good teams that both want to be champion in a mostly just manner. While I understand that it feels right to give a team an edge for success it maintained over the long haul in the regular season, full homefield advantage in a single knockout game is too blunt of a tool to accomplish this, and further due to the nature of the league’s parity and the odd imbalanced scheduling, I’m not sure there’s much between 1-4 that would make me even want to dole out rewards/advantages in the playoffs between those teams. Just let the playoffs be what playoffs are supposed to be, taking the X number of best teams over the course of the year and facing them off against each other to determine who can come out on top when it matters most.

Postscriptum:

I realize that I didn’t address the MLS Cup Final being hosted by the higher seed as well as the play-in games being single elimination games hosted by the 3/4 seeds vs 5/6 seeds in each conference. For the record, it would be ideal to host the MLS Cup Final on neutral ground (like the Super Bowl), but I understand how ticket sales / tv optics impact this decision for a league that’s still trying to establish it’s place. It seems a necessary evil to me to make sure the Final is sold out and packed. Similarly, I think it’s fair to think of the 5th and 6th best teams in a conference as “wild cards” lucky enough to have made it into the playoffs (but also important that they’re allowed a path at all, given a league of high parity demands more teams be allowed entrance into the postseason).

Additional Material on Home Advantage:

Sorry for the team-agnostic content this time around. Will try to do a catch up post soon on recent ATL UTD matches… there’s just so many of them, and some of them are weird.

Atlanta United FC 3 – 0 FC Dallas

Chance Dominance & Efficiency in the Final Third

In the first ever soccer match at Mercedes Benz Stadium, Atlanta dominated the score sheet with a 3-0 victory and created their highest single game tally of expected goals (2.8 per ASA) this season. The team held FC Dallas to 0 goals and 1.2 expected goals (this spread is partly luck and partly Guzan). And the resulting 1.7 xGD is the highest winning expected goal difference for the club this season. All this points to dominance by the Five Stripes, and I think that’s probably fair. The box score suggests dominance as well:

Game Stats

However, I would say as a fan, I only felt comfortable in the second half. FC Dallas’ only two shots on target were two very good chances that Guzan had to make big saves for.

FCD on target and blocked
Green (SOT) early in 2H. Yellow (blocked) all in 1H.

And as dominant as Atlanta were in the end, those types of games will occasionally go south depending on the ordering of events and the direction of some bounces. I’ve included a map of all 5 of FC Dallas’ shots on target and blocked shots. They’re all very good chances, and would’ve altered events.

 

On the Atlanta side of things, 12 of 19 shots being put on frame is a high number (63% vs the league average 36%). The home side were exceedingly efficient at turning shots into #problems for Jesse Gonzalez. But as I recall, they were also much more efficient at turning attacks into shots (contrast this with away at Orlando where many counters and other attacking moves ended up just shy of registered shots). Touches Around Box - ATLWhoscored has Atlanta at 27 touches inside the box, with an insanely high 8 firing within the 6 yard box. While a few of the 19 were from range, 19 shots on 27 touches inside the box feels pretty high to me – it feels *very* efficient. Because of all of this, I would not describe Atlanta’s 25% SOT conversion in this game as wasteful or as evidence of “sloppiness in the final third.” I would say the team were mostly lights out efficient in turning attacks into threats and threats into huge threats. Jesse Gonzalez stood on his head some, but at the same time, even while putting on massive shots and xG numbers, Atlanta still bested the 2.8 expected goals with 3 actual goals. I would say finishing was not a problem in this one.

That all being said, while it’s not surprising to hear very bullish talk of the team challenging for a top 2 spot in the east, along with talk that the wider and deeper playing surface has offered us a glimpse at a new normal for Atlanta where they will dominate every away side with pace and tenacity, (inhales) I expect we might see the team be slightly less efficient going forward at turning attacks into shots, slightly less efficient at turning shots into shots on target, and slightly more efficient at turning shots on target into goals (as has been the trend so far this year). I don’t feel too strongly about it. I’m just hesitant to think that what we saw against FC Dallas is what we’ll see going forward because of a bigger field and a slicker surface.

Pressing & Tidiness

Pressure FCD Table.PNG

These pressing numbers seem fairly standard for Atlanta with the exception that Dallas was slightly tidier than a typical Atlanta opponent. This may have been impacted by the severe game states of Atlanta leading for most of the game and increasing its lead as the game went on. Also both teams played more own-half passes than I’ve been seeing in these numbers. Atlanta’s 225 higher than its season average of 195, and FC Dallas’ 163 higher than Atlanta’s opponents’ average of 126. Perhaps this is the bigger pitch showing up, hard to tell. I thought Atlanta’s press was somewhat more ruthless than these numbers show with several balls won back quickly after a turnover, and quickly converted into through balls and other transition moves.

Atlanta’s defensive actions in the first half (left) and second half (right):

This is somewhat surprising given what I thought I observed which was a press that slowed somewhat in the second. I think in the second what you’re seeing is more counter-pressing — pressing to win the ball shortly after losing it to keep Dallas from countering.

Shape

We saw a return to the more pronounced back-3 shape with Larentowicz eager to join the other centre backs when in possession (LGP and Parkhurst in the left graphic, Jeff in the right).

Asad and Almiron seemed to connect over and over again with great effectiveness on the left. I can’t tell just yet if we should credit the larger pitch or not. It very well could have been the case that they each felt more comfortable on the ball with the defense stretched both laterally and vertically by the speed of Martinez and Villalba (and also Almiron). Jason Poon suggested that Atlanta and Almiron specifically targeted Dallas’ right back Grana. And that might very well have been the case. On the left below is the chalkboard for Garza + Asad, and on the right the map for Almiron, who does seem awfully left-leaning for a central playmaker. Asad drifts inward some but no more than usual. Anyhow, the key passes coming in from that side from these 3 players alone is … it’s high.

Walkes and VillalbaOn the right side, there has been some criticism recently that the Garza/Asad dynamic of the fullback stretching the defense wide and the attacking midfielder tucking in wasn’t being replicated to the same degree of success. In this game however, I noticed Villalba tucking in often nicely into pockets between the lines to receive the ball. We don’t see the same degree of advancement from Walkes that we might see from Garza game to game, but the variety in attacking width on the right seemed to work well enough.

 

 

One last look at the attacking passes for each team. You can really see a contrast in style between the two. The first half below, Atlanta on the left and Dallas on the right:

FC Dallas obsessed with width. Atlanta just killing them from the most dangerous areas. In the second, it’s a little bit more varied as Dallas chased the game.

I’ll have to cut this one off now. Too many games.

In short, this game was a lot of fun. It’s possible the larger pitch is super-charging the team, but I want more evidence before we call that one. Atlanta was extremely efficient at turning attacks into shots, but Gonzalez was also a disruption. Guzan was very good. Atlanta good. Dallas bad.

 

 

Atlanta United & MLS Roster Rules: 2018 Salary Cap Scenarios

Just a quick jump post over to DirtySouthSoccer where I wrote a piece about the MLS roster rules and the salary cap, looking ahead to 2018 and wondering what sort of options the front office has to retain the squad as currently assembled. If you like spreadsheets, give it a read, but maybe make a pot of coffee first.

I try to guess at GAM and TAM balances as initially allocated to the expansion clubs plus I guess at undisclosed traded amounts and unconfirmed rumors of future money injections by the league. In the end, if you want to help think through whether the club can sign Garza and/or Asad next year, you’ll need to read most of it.

2018 Roster Panic Part 2: Lost in Spreadsheets

Catch-up Post: OCSC-II, SKC, DCU, PHI

This will be quick and fairly devoid of game analysis content, but just wanted to make sure I dropped in the pressing/tidiness and chance creation figures for the last several Atlanta United matches that I hadn’t touched on here, matches in which the Five Stripes tallied 3 points in 3 away games and 1 home game. Not great honestly if you like the idea that good teams should win at home and draw away (3 out of 6 expected points in that case). Combine it with the stolen 3 in Orlando and you’re at 6 of an expected 7, with some luck.

8-30 last 4 press
Expected goals numbers come from @analysisevolved at AmericanSoccerAnalysis.com

I would suggest the somewhat troubling thing is that on average these last 4 games look on average like the rest of the season in terms of pressing and tidiness. Atlanta are generally giving away 30+ moments in their own half, and disrupting their opponents just shy of the season average 30 mark. They’re creating a couple more shots per game but not creating excess expected goals outputs from those shots, suggesting a shift towards higher volume / lower quality – slightly away from the successful albeit rare profile they’ve ridden all season with excessive finishing on a smaller number of chances. Without looking closer, I have a hunch just from what I’ve seen that Atlanta are suffering more blocked shots than previously, which would also line up with this shift. Why this is happening despite the general steadiness in pressing disruption is unclear. Perhaps it is some game-state stuff, Atlanta chasing the game for good portions of these last 4 games, and shooting against defenses that are more solidly in place (even with some red card action).

I should also mention that to my eye, the press was hit or miss during this period. Against SKC, I felt the team really failed to turn Sporting over in their own half (and the numbers do show this). But the other three, ATL kept that attempt per giveaway number really low for their opponents.

For those interested, here are the individual match pressing/tidiness breakdowns by half:PressureTablePress SKCPressureDCU3PressurePHI

The Kansas City match stands out as one of the rare instances this season where Atlanta were mostly outplayed.

That’s about it for now.

Though while I’m here, I’ll go ahead and link to some things I’ve written recently for DirtySouthSoccer:

Atlanta United and Finishing Chances

Finishing. This is not the fist time I’ve approached this topic on this here blog. But as we drive deeper into the season, it’s an increasingly difficult topic to ignore for Atlanta. While its easy to lament missed chances and their impact on points dropped in the table (think of DC home match), the truth is that Atlanta United are a statistical outlier, finishing an exceptionally high percentage of their chances relative to the rest of the league, and outperforming their expected goals by the widest margins we’ve seen in MLS. It begs the question…

When it comes to converting shots into goals, are Atlanta luckier than most or better than most? Stick around. I have charts!

Background:

Evidence has shown that in soccer, consistently creating good chances and limiting your opponent’s chances is a key success factor. The rate at which your chances are converted into goals may come and go, but whatever it is that you do that creates more and better chances and limits the quantity and quality of your opponent’s chances is the secret recipe, the valuable IP that makes a team good. In fact when trying to predict a team’s future performance, the number and quality of its past goal scoring chances compared to those of its opponents is more often a better predictor than its past goal differential.

And it’s because of this that when you see a team with an exceptionally high shot conversion rate, you are supposed to be worried that the team will perform worse in the future than it has in the past — that its past results are due in large part to something that won’t be repeated in the future (chance). This fear could be comforted if the team were taking higher probability shots than the rest of the field (the sort of thing you might measure by looking at the team’s expected goals per shot – EDIT: STOP WHAT YOU’RE DOING AND WATCH THIS VIDEO), but generally speaking high conversion percentages are red flags.

Atlanta United’s historically high shot conversion and exp. goals over-performance

Atlanta United has an exceptionally high shot conversion rate. And it has achieved this all season long. Atlanta are on top of almost every flavor of shot conversion chart (shots, shots on target, open play shots, etc). As an example, immediately below is the shot on target conversion metric through the 21 games or so in 2017:SOTConv

And here are the shots on target conversion rates for all teams from 2012 – 2017 YTD:SOT conversion

So it’s not just the highest SOT conversion rate in MLS at the moment, but it is historically high (only 2014 Dallas and 2013 Red Bulls top Atlanta’s 2017 figure), although curiously a few teams this year are also very high . Does Atlanta have a high shot quality per shot (xG/shot) number to prop up this high conversion percentage? No, they don’t. It’s middling at best. See a helpful graphic of MLS shot quality and volumes from AmericanSoccerAnalysis here. Another way of looking at this is to look at Atlanta’s goals scored compared to their expected goals. Atlanta are averaging 1.9 goals per game against an expected goals per game figure of 1.3. They’ve scored 15 more goals (41 vs 26) than MLS teams historically have based on the volume and location and other attributes of the shots they have taken (based on publicly available data). And again to prove the point, this will look familiar, but here’s how Atlanta looks historically in terms of their goals scored above expected goals per game (it is the highest recorded):G-xG all years

In Search of an Answer

So what do we say about this? As we’ve discussed before on the blog, the possibilities seem to be as follows, and a combination of these is likely:

  1. Atlanta are luckier than most.
  2. Atlanta are more skilled at shooting than most.
  3. Atlanta are taking better shots than most, which is propping up the high conversion number; however, the models we have for measuring shot quality (expected goals) are struggling to properly value the particular shots Atlanta are taking.

Shot Accuracy (also historically high)

Quickly, on #2: Skill, I’d like to point out that not only are Atlanta putting a higher percentage of their on-target shots past the goalkeeper, they are also putting a higher percentage of their shots … on target — testing the keeper at a higher rate than anyone else. And while, like shot conversion percentages, this isn’t a perfectly repeatable stat (repeatability suggests skill is involved), it is more repeatable than conversion. First, here’s the shot accuracy of 2017 MLS teams (shots on target / shots). Atlanta kills it.ShotAccSome pretty good teams at the top, but some also dispersed throughout if I’m honest. And below are the shot accuracy rates by team from 2012 to 2017 YTD:Historic Acc

Once again, that’s historically high. Only the 2015 Sounders put a higher percentage of their shots on target. And again curiously, another 2017 team is right there with Atlanta, this time the Fire.

I’m tempted to suggest this very high accuracy number is evidence of either #2 (shooting skill) or #3 (Atlanta’s chances being better than the models suggest). I can’t really prove that first idea but it seems plausible. The second one — I don’t know — I think I remember something about shots on target including some bit of embedded information about the quality of the chances (since its easier to put a high quality chance on target than a low quality one). To my eye, watching the team, it doesn’t feel like they are lucking into a high percentage of shots on target. The team really seems to prefer to not shoot until they’ve set up an open look. Many good opportunities end before a shot is generated as the team works to find a better shot by passing or dribbling — this sounds a little bit like *gaming xG* but I can’t be too sure.

Shot Openness: Dissecting all the goals

I haven’t looked at every single shot taken this year by the Five Stripes, but if we look at all the goals (yep all of them, many of them here: thanks Whitecaps), a very high percentage of these are 1v1 against the keeper (and several are empty net opportunities), or there are very few opposition outfield players between the shooter and the keeper. This type of “openness” of a shot has a big impact on its chance conversion, but most expected goals models can only “guess” at the the openness of a shot based on other event data context. They don’t “see” the openness, but they might see that the shot was assisted by a through ball or that the buildup was defined as a “fast break.” I tried to record a bunch of admittedly judgmental shot quality attributes for all these goals. See below for a summary of what I compiled watching every goal, looking out for certain “openness” attributes and then I’ll compare it to another team:

Shots through 22

I haven’t done this for all MLS teams because of time, but what jumps out to me are the 26 1v1 chances, and the 35 chances with 1 defender or fewer between the shooter and the keeper/goal. My gut is that these figures are high compared to the league average (which I do not know). For comparisons sake, I picked another team, New York Red Bulls and gave them the similar treatment of watching every goal scored and capturing “openness data.” I chose them for two reasons, first they are currently running neck and neck with Atlanta for the 4th seed in the playoffs (and a first round home match), and secondly (and more importantly), they are an example of a very good team that’s not crushing its expected goal numbers like Atlanta is. In fact they are slightly under-performing. So I was interested to see if there’s a significant difference in the composition of the goals scored. There is.

NYRB Goals

Across the board NYRB’s goals feature slightly fewer “openness” attributes, except they do a great job of finding BWP in the 6 yard box. If we compare them side by side it’s somewhat easier to see.

ATLNYRB

Is this the difference between a team overperforming its expected goals by historic margins (+0.6/game) and a team slightly underperforming its expected goals (-0.11/game)? Here are the distributions of defenders in between the shooter and the keeper for Atlanta vs Red Bulls.

 

Again, we can feel confident it’s either 1) chance/luck and Atlanta really aren’t as good in attack as the results show, 2) Shooting skill with Atlanta being better at finishing than most other teams, or 3) the quality of Atlanta’s chances (primarily related to their “openness”) not being picked up in the event data based expected goals models.

I would suggest it is a mixture of all three with the above “goal quality attributes” hinting gently towards #3. And perhaps Atlanta’s three designated players being signed into the attacking front 4 hinting gently towards #2.

Let me know your thoughts. What am I missing?

I should note that watching all of a team’s goals is a fairly weak attempt at trying to identify other shooting attributes that might be contributing to outliers in shooting efficiency and that looking at every single shot would be a much better exercise (and even still a flawed one). But I don’t know how to get the footage and honestly I don’t know if I could do it. This is at least something. I think it’s better than throwing one’s hands up and saying “welp, Atlanta are lucky” or “welp, Atlanta are master finishers.”

Expected goals data comes from AmericanSoccerAnalysis. If you read this regularly you probably know that by now.

Post credits Scene hinting at more shared universe titles to come

While I was digging through finishing metrics (primarily goals minus expected goals figures), I noticed something interesting that I’m not sure how to interpret. There’s reason to believe its further proof that there’s significant “openness” of shots not being appropriately valued by expected goals models. Basically, if you look at G-xG distributions between home and away matches you see notable differences. The home distributions stretch out more positively with large totals of significant overperformance games showing up whereas the away matches look more like a normal distribution but tilt slightly in the direction of under-performance.

 

 

If you take all these distributions as a percentage of the total and chart the differences in percentage share by bin between home and away you get the below image, which more clearly shows the lean towards an over performance in finishing for the home team relative to the away team.2017 home away bins 10

 

This is 2017 data for all MLS teams over 22 or so weeks of the MLS season, so it’s a good number of games and it runs the full spectrum of good and bad teams. It would suggest that either 1) teams shoot better at home, or 2) when playing at home teams get better chances than the models are able to capture in xG. The first should be dubious to anyone that thinks finishing generally averages out across all shots. The second one makes more sense with what we know about home field advantage in MLS, that it definitely exists. It doesn’t seem too wild to think that teams create better chances at home, and perhaps even chances that are better than the expected goals models give them credit for. But that’s just 2017 data. What does the 2011-2017 data show? Well, it’s both a) much less pronounced (smaller differences between bins between home and away), and also b) home teams seem to both significantly over-perform and significantly under-perform more often than away teams. 2011-2017 home away bins 10

So that leads us back to something strange going on in 2017, which could very well be a skew driven by Atlanta United, or a shift in the landscape of finishing for MLS in 2017, or an increase in the types of good chances that are undervalued by models? Or… variance working its way out over the course of a full season.

Appendix: Assorted resources on finishing skill in football

https://cartilagefreecaptain.sbnation.com/2014/4/25/5652640/player-finishing-skill-is-real

http://www.optasportspro.com/about/optapro-blog/posts/2014/on-the-topic-of-expected-goals-and-the-repeatability-of-finishing-skill.aspx

http://statsbomb.com/2014/03/thinking-about-finishing-skill/

http://www.optasportspro.com/about/optapro-blog/posts/2017/blog-re-examining-finishing-skill/

http://statsbomb.com/2017/07/quantifying-finishing-skill/

http://www.americansocceranalysis.com/home/2016/4/4/does-finishing-skill-matter-in-mls?rq=finishing

http://www.americansocceranalysis.com/home/2016/10/18/is-finishing-real-heading-towards-a-conclusion?rq=finishing

There are many others out there, plus I’ve discussed it occasionally in ATL match previews and recaps on this blog.