Park Effects: How does this apply in MLS?

This sparked my curiosity the other day. Joe Posnanski, who is an amazing baseball writer, wrote about the current MVP race as the MLB season dwindles down. One of his large points is, of course, offensive production and how you properly place that into context. He mentions something about park factors between the two hitters in the race, young stud Mike Trout and hall-of-fame surefire Miguel Cabrera. As usual, this discussion of value in baseball spawned chaos in the comments section and lead to a follow-up article.

JoePo breaks down park factors crudely but effectively in stating the following:

But the BASICS of Park Factors are the easiest thing imaginable.

All you do is this:

Step one: You take the average runs scored in a ballpark (both teams).

Step two: You take the average runs scored in that team’s road games (both teams).

Step three: You divide the first total by the second.

And that’s all. Park Factors. There is so much contentiousness about Comerica Park but it’s all simple math. This year, the Tigers have scored 355 runs at Comerica and allowed 275 runs. That’s a total of 630 runs in 67 games — 9.4 runs per game.

Now, this was brought to my attention by Tom Tango and his mention on his blog. Tango also gives some brief qualifiers that are specific to baseball, as well as mentioning the uncertainty of the exact degree that it affects the race. It’s some great stuff for baseball.

It made me start wondering about park conditions in MLS. It’s obvious that pitches play differently and that they come in different shapes and sizes. This can be done a multitude of ways as mention by Poz and described by Basellball-Reference. It’s already been covered one way by Alex Olshansky of Tempo-Free Soccer in an article for StatsBomb a month ago.

However, Alex used Goal differential. Which is fine, if we’re strictly speaking about an individual park leading to more goals, not necessarily home field advantage. I wrote an article just a month ago about home field advantage working off percentage of points won at home versus total points.

Regardless, you can see most teams seem have an advantage playing at home. But I’m interested in how many of these home locations either increase limit or increase shots/goal opportunities. Is there a place in MLS that, due to the dimensions or the crowd or some other outside reason, it is better to be a striker versus a defender? That it limits or maybe creates more goal scoring opportunities?

It’s an interesting question for certain and maybe not even one to limit to goals. Maybe we could open it up to turnovers, as that might give us some indication of the quality of the pitch. These are just some thoughts on a Friday afternoon.

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MLS, Home Field Advantage And Success Rates

This week on the podcast we talked a bit about home field advantage and the fact that it undeniably exists. But while it does exist, the question then becomes to what extent does it exist? What teams have taken advantage of it over the past few years? I went back as far as 2008 to collect some data. I’m not sure what this data all means, but I feel that it, at the very least, gives us a bit of commentary on those teams that had success and failure on their home pitches.

I broke clubs into two groups: teams that scored more than 40 points and teams that scored less than 40 points. Then I compiled some key home stats for the two groups.

A quick key for the stats used:

%home won, is the percentage of possible games at home at the team won. Duh, right?

%home points is the percentage of its home games in which the team nabbed any points (draw or win).

%total of points is how many points from home games contributed to their total points accrued over the season.

Then GD is just goal differential.

Team Above 40 Points

2008
POS TEAM GP W D L F A Home Points Total Points %home won %home points %total of points Home- GD GD
1 Houston 15 10 4 1 30 14 34 51 66.67% 93.33% 66.67% 16 13
2 Chivas USA 15 7 4 4 21 15 25 43 46.67% 73.33% 58.14% 6 -1
3 Real Salt Lake 15 8 6 1 24 10 30 40 53.33% 93.33% 75.00% 14 1
POS TEAM GP W D L F A Home Points Total Points %home won %home points %total of points Home- GD GD
1 Columbus 15 11 2 2 30 15 35 57 73.33% 86.67% 61.40% 15 14
2 Chicago 15 7 3 5 23 17 24 46 46.67% 66.67% 52.17% 6 11
3 New England 15 6 4 5 24 20 22 43 40.00% 66.67% 51.16% 4 -3
4 Kansas City 15 9 4 2 22 15 31 42 60.00% 86.67% 73.81% 7 -2

Team Below 40 Points

2008
POS TEAM GP W D L F A Home Points Total Points %home won %home points %total of points Home- GD GD
5 New York Red Bulls 15 9 3 3 30 20 30 39 60.00% 80.00% 76.92% 10 -6
6 DC United 15 9 2 4 32 19 29 37 60.00% 73.33% 78.38% 13 -8
7 Toronto FC 15 6 7 2 17 12 25 35 40.00% 86.67% 71.43% 5 -9
POS TEAM GP W D L F A Home Points Total Points %home won %home points %total of points Home- GD GD
4 Colorado 15 7 3 5 22 14 24 38 46.67% 66.67% 63.16% 8 -1
5 FC Dallas 15 5 6 4 23 19 21 36 33.33% 73.33% 58.33% 4 4
6 San Jose 15 6 4 5 22 19 22 33 40.00% 66.67% 66.67% 3 -6
7 Los Angeles 15 6 5 4 35 27 23 33 40.00% 73.33% 69.70% 8 -7

Team Above 40 Points

2009
POS TEAM GP W D L F A Home Points Total Points %home won %home points %total of points Home- GD GD
1 Columbus 15 9 4 2 25 15 31 49 60.00% 86.67% 63.27% 10 10
2 Chicago 15 5 6 4 16 17 21 45 33.33% 73.33% 46.67% -1 5
3 New England 15 7 4 4 22 16 25 42 46.67% 73.33% 59.52% 6 -4
4 DC United 15 7 5 3 19 14 26 40 46.67% 80.00% 65.00% 5 -1
POS TEAM W D L F A Home Points Total Points %home won %home points %total of points Home- GD GD
1 Houston 15 8 6 1 23 13 30 48 53.33% 93.33% 62.50% 10 10
2 Los Angeles 15 7 4 4 18 17 25 48 46.67% 73.33% 52.08% 1 5
3 Seattle Sounders FC 15 7 6 2 21 10 27 47 46.67% 86.67% 57.45% 11 9
4 Chivas USA 15 9 3 3 25 14 30 45 60.00% 80.00% 66.67% 11 3
5 Real Salt Lake 15 9 5 1 34 11 32 40 60.00% 93.33% 80.00% 23 8
6 Colorado 15 8 5 2 25 10 29 40 53.33% 86.67% 72.50% 15 4

Team Below 40 Points

2009
POS TEAM GP W D L F A Home Points Total Points %home won %home points %total of points Home- GD GD
5 Toronto FC 15 8 4 3 20 14 28 39 53.33% 80.00% 71.79% 6 -9
6 Kansas City 15 4 5 6 18 20 17 33 26.67% 60.00% 51.52% -2 -9
7 New York Red Bulls 15 5 4 6 24 20 19 21 33.33% 60.00% 90.48% 4 -20
POS TEAM GP W D L F A Home Points Total Points %home won %home points %total of points Home- GD GD
7 FC Dallas 15 8 4 3 28 19 28 39 53.33% 80.00% 71.79% 9 3
8 San Jose 15 6 4 5 22 21 22 30 40.00% 66.67% 73.33% 1 -14

Team Above 40 Points

2010
POS TEAM GP W D L F A Home Points Total Points %home won %home points %total of points Home- GD GD
1 New York Red Bulls 15 10 2 3 18 9 32 51 66.67% 80.00% 62.75% 9 9
2 Columbus 15 10 2 3 22 12 32 50 66.67% 80.00% 64.00% 10 6
POS TEAM GP W D L F A Home Points Pts %home won %home points %total of points Home- GD GD
1 Los Angeles 15 9 2 4 27 19 29 59 60.00% 73.33% 49.15% 8 18
2 Real Salt Lake 15 11 4 0 31 7 37 56 73.33% 100.00% 66.07% 24 25
3 FC Dallas 15 8 6 1 25 13 30 50 53.33% 93.33% 60.00% 12 14
4 Seattle Sounders FC 15 8 3 4 21 16 27 48 53.33% 73.33% 56.25% 5 4
5 Colorado 15 8 5 2 26 11 29 46 53.33% 86.67% 63.04% 15 12
6 San Jose 15 7 3 5 17 14 24 46 46.67% 66.67% 52.17% 3 1

Team Below 40 Points

2010
POS TEAM GP W D L F A Home Points Total Points %home won %home points %total of points Home- GD GD
3 Kansas City 15 7 3 5 25 19 24 39 46.67% 66.67% 61.54% 6 1
4 Chicago 15 4 7 4 14 13 19 36 26.67% 73.33% 52.78% 1 -1
5 Toronto FC 15 6 6 3 19 15 24 35 40.00% 80.00% 68.57% 4 -8
6 New England 15 7 3 5 21 18 24 32 46.67% 66.67% 75.00% 3 -18
7 Philadelphia Union 15 6 6 3 22 16 24 31 40.00% 80.00% 77.42% 6 -14
8 DC United 15 3 1 11 12 25 10 22 20.00% 26.67% 45.45% -13 -26
POS TEAM GP W D L F A Home Points Total Points %home won %home points %total of points Home- GD GD
7 Houston 15 6 3 6 25 21 21 33 40.00% 60.00% 63.64% 4 -9
8 Chivas USA 15 6 2 7 19 19 20 28 40.00% 53.33% 71.43% 0 -14

Team Above 40 Points

2011
POS TEAM GP W D L F A Home Points Total Points %home won %home points %total of points Home- GD GD
1 Sporting Kansas City 17 9 6 2 29 51 52.94% 88.24% 56.86% 10
2 Houston Dynamo 17 10 4 3 33 49 58.82% 82.35% 67.35% 4
3 Philadelphia Union 17 7 9 1 22 48 41.18% 94.12% 45.83% 8
4 Columbus Crew 17 9 5 3 30 47 52.94% 82.35% 63.83% -1
5 New York Red Bulls 17 8 6 3 27 46 47.06% 82.35% 58.70% 6
6 Chicago Fire 17 6 8 3 21 43 35.29% 82.35% 48.84% 1
POS TEAM GP W D L F A Home Points Total Points %home won %home points %total of points Home- GD GD
1 LA Galaxy 17 12 5 0 36 67 70.59% 100.00% 53.73% 20
2 Seattle Sounders FC 17 9 4 4 31 63 52.94% 76.47% 49.21% 19
3 Real Salt Lake 17 10 4 3 33 53 58.82% 82.35% 62.26% 8
4 FC Dallas 17 9 3 5 32 52 52.94% 70.59% 61.54% 3
5 Colorado Rapids 17 6 9 2 20 49 35.29% 88.24% 40.82% 3
6 Portland Timbers 17 9 3 5 32 42 52.94% 70.59% 76.19% -8

Team Below 40 Points

2011
POS TEAM GP W D L F A Home Points Total Points %home won %home points %total of points Home- GD GD
7 DC United 17 4 8 5 20 39 23.53% 70.59% 51.28%
8 Toronto FC 17 5 8 4 23 33 29.41% 76.47% 69.70%
9 New England 17 4 6 7 18 28 23.53% 58.82% 64.29%
POS TEAM GP W D L F A Home Points Total Points %home won %home points %total of points Home- GD GD
7 San Jose 17 5 8 4 23 38 29.41% 76.47% 60.53%
8 Chivas USA 17 5 5 7 20 36 29.41% 58.82% 55.56%
9 Vancouver Whitecaps 17 6 5 6 23 28 35.29% 64.71% 82.14%

Team Above 40 Points

2012
POS TEAM GP W D L F A Home Points Total Points %home won %home points %total of points Home- GD GD
1 Kansas City 17 10 4 3 22 12 33 63 58.82% 82.35% 52.38% 10 15
2 DC United 17 12 4 1 37 17 37 58 70.59% 94.12% 63.79% 20 10
3 New York Red Bulls 17 11 4 2 34 18 35 57 64.71% 88.24% 61.40% 16 11
4 Chicago 17 11 3 3 27 18 36 57 64.71% 82.35% 63.16% 9 5
5 Houston 17 11 6 0 31 12 33 53 64.71% 100.00% 62.26% 19 7
6 Columbus 17 11 3 3 28 21 36 52 64.71% 82.35% 69.23% 7 0
7 Montreal Impact 17 10 3 4 31 19 34 42 58.82% 76.47% 80.95% 12 -6
POS TEAM P W D L F A Home Points Total Points %home won %home points %total of points Home- GD GD
1 San Jose 17 10 6 1 43 22 31 66 58.82% 94.12% 46.97% 21 29
2 Real Salt Lake 17 11 2 4 27 15 37 57 64.71% 76.47% 64.91% 12 11
3 Seattle Sounders FC 17 11 2 4 27 11 37 56 64.71% 76.47% 66.07% 16 18
4 Los Angeles 17 10 1 6 31 20 36 54 58.82% 64.71% 66.67% 11 12
5 Vancouver Whitecaps 17 8 6 3 25 17 27 43 47.06% 82.35% 62.79% 8 -6

Team Below 40 Points

2012
POS TEAM GP W D L F A Home Points Total Points %home won %home points %total of points Home- GD GD
8 Philadelphia Union 17 7 2 8 22 20 23 36 41.18% 52.94% 63.89% 2 -8
9 New England 17 7 6 4 23 15 27 35 41.18% 76.47% 77.14% 8 -5
10 Toronto FC 17 3 5 9 15 25 14 23 17.65% 47.06% 60.87% -10 -26
POS TEAM GP W D L F A Home Points Total Points %home won %home points %total of points Home- GD GD
6 FC Dallas 34 6 8 3 21 16 26 39 17.65% 41.18% 66.67% 5 -5
7 Colorado 34 8 3 6 29 19 27 37 23.53% 32.35% 72.97% 10 -6
8 Portland Timbers 34 7 6 4 24 21 27 34 20.59% 38.24% 79.41% 3 -22
9 Chivas USA 34 3 3 11 9 30 12 30 8.82% 17.65% 40.00% -21 -34

2008-2012 average, Teams above 40 points

avg HP avg TP avg %HW avg %HP avg %of TP
25 41 46.10% 68.59% 50.56%

2008-2012 average, Teams below 40 points

avg HP avg TP avg %HW avg %HP avg %of TP
24 35 37.67% 67.26% 71.09%

There are a few things that I think you could really take from this, starting with A) there is so much parity in this league that it doesn’t matter if you are a good team or a bad, a game at home should give you a lot of confidence. B) Good teams, play-off teams, teams who want a chance at the Supporters Shield … they win road games. The teams above 40 points and teams below 40 points are only separated by their percentage of total points won at home. Meaning that teams above 40 points only took 50% of their teams total points from home games; they won on the road, too. Where as teams that struggled depended on those home games to make them suck less.

Good teams win at home, but so do bad teams… unless you are DC United. Sorry, Drew.

Field Dimension, Turf and Home Field Advantage in MLS

During last weekend’s podcast, we discussed home field advantage and where it might come from. There is much literature to suggest that home field advantage comes largely from rowdy home crowds—crowds that both encourage the home team to be more aggressive and encourage the referees to be more biased—but you probably already presumed that.

We went on to talk about “home specialists,” or teams that play especially well at home in a given season. An article on the site The Power of Goals theoretically explains why home specialists from any single season tend to be products of statistical noise rather than signal. That’s not to say there aren’t home specialists out there, only that it is nearly impossible to identify them statistically in a single season.

Picking out the teams that have performed markedly better at home, and then retroactively seeking explanations to match the traits of those teams is known as cherry picking, and it’s likely to lead to false conclusions (On the podcast, I recounted an example from the book Naked Statistics by Charles Wheelan as to why this can lead to trouble). Instead, identifying traits of teams and stadia first, and then checking for measurable differences in home performance based on those traits is a more sound approach.

We have mentioned around here before that Houston’s narrow home pitch might have helped the Dynamo to one of the best home records since BBVA Compass Stadium was built in preparation for the 2012 season. Indeed, Houston’s field is the narrowest in the league at 70 yards, and the Dynamo’s home goal differential is a whopping 1.33 goals better at home than on the road. However, the only reason we considered field dimensions was because Houston has performed so well at home.

We went like this:

Extreme split for Houston –> Field Dimensions must matter

But we should have thought like this:

Field Dimensions –> Extreme splits?

To advance the discussion, I gathered data going back to the 2010 season in order to look for explanatory patterns in two observable variables of stadia: field dimensions and surface. If teams are able to train on especially large or especially small fields, or on turf, such differences in the pitches may give home teams a leg up in matches played on those familiar pitches.

It turns out there is not enough evidence that either turf surfaces or field dimensions have much to do with home success.

Surface vs. Home success

There are currently four teams that play on turf: Portland, Seattle, Vancouver and New England. While the Timbers and Whitecaps have dominated at home, The Sounders and Revs have been sub par relative to the league in that department. Considering I didn’t account for the confounding variable that two of these teams play in front of some of the rowdiest fans in MLS, the “turf effect” may not even exist at all. It’s hard to say with only four teams playing on turf, three of which are not even in their adolescence as franchises.

Width vs. Home success

Field dimensions showed minimal effects, as well. Though Houston’s small, 70-by-115-yard pitch has correlated with its home success, that correlation is not true of other small stadia. The next-smallest stadium can be found in Washington D.C.,** but DCU has actually performed a little worse at home relative to the typical league splits. Montreal has the widest pitch at 77 yards, and yet, also has performed well. There is a chance that teams with extreme widths—extremely narrow or extremely wide—have some sort of advantage, but we’re going to have to wait for additional data from Houston and Montreal to be more definitive about that.

The vast majority of MLS pitches, 16-of-19 in fact, are either 74 or 75 yards wide. So even the two extremes in Houston and Montreal are not all that different. Houston could be a team built to play on a narrow pitch, but I’m skeptical that A) Soccer Analytics have come far enough for a general manager to sort that out and B) that 4-5 yards would make such a big difference.

Though I can’t say for sure that the pitch effects are non-existent, I can say pretty confidently that they aren’t pronounced or noticeable in a single season. Right now, I would argue it’s more likely that Montreal and Houston have performed so well at home due to the random variation of only two seasons of data. We will have to wait another few seasons to check on that one.

*Vancouver plays on Astroturf while the other three play on Field Turf.

**DCU’s field at RFK is a little wider at 72 yards, and actually a little shorter at 110 yards.