I'm originally a baseball guy. Home field advantage isn't really a big deal in baseball. Being charitable to the home team, in MLB history, the home team wins about 55% of the time. It's an edge, but it's pretty small.
So last year while World Cup qualifying was going on, I looked at some of the home/away stats and it was astonishing. Considering that everyone plays on a rectangular field with the same-sized rectangular goals, it's pretty crazy the kind of home field advantage that you see. What I had found at that time (these are now out of date) was:
CONCACAF goals scored per game home/away:
rd4: 2.00/0.86 (in progress)
South America (all on one big table)
Europe (first round with 9 groups)
Now, there are all sorts of ways to overreach from that data and try to draw too many conclusions, but it does make it seem as though length of travel (and ease of travel) could be one of the biggest things that drives HFA in soccer.
Anyway, knowing that this is a rather huge issue in international soccer, I figured I would look at some CONCACAF Champions League/Cup data to see what it's been like for club play in the region. To quantify home-field advantage (HFA) in CONCACAF play, I decided to look at all games involving MLS teams over the last 9 incarnations of the tournament. This goes back 10 years, but there was no 2001 Cup, and I'm not including this year's results because teams aren't even on home/away games.
First, I'll break it down in terms of MLS teams vs. Mexican or non-Mexican sides.
So, basically, MLS teams do extremely well at home against anyone that's not from Mexico, though they don't score a whole lot considering how often they win and how rarely they lose. On the flip side of the coin, MLS teams haven't won in Mexico and with 3.24 goals against per game, they've been absolutely dominated.
What does it look like if we break each country out separately?
One row that really stands out to me is the 1-8-1 vs. Costa Rica in Costa Rica. 0.40 PPM is nearly as bad as the 0.12 PPM that MLS teams have in Mexico.
The other thing that sticks out to me is that teams from every single country--even some countries which have a pretty small sample--have better results, mostly by a wide margin, at home than on the road.
From a Sounders point of view, I think it's interesting to look at the Sounders' results in light of these typical MLS results.
at Honduras -- 1.4 PPM, most common result: (toss up between win and loss, let's call it a Draw)
vs. Mexico -- 1.35 PPM, most common result: (toss up between win and loss, call it a Draw again)
at Costa Rica -- 0.40 PPM, most common result: Loss
at Mexico -- 0.12 PPM, most common result: Loss
vs. Honduras -- 2.40 PPM, most common result: Win
vs. Costa Rica -- 1.70 PPM, most common result: Draw
Considering that the first two scheduled matches have historically been a fairly even split between win and loss, say you would generally expect the Sounders to get 3 points there, no points in their next two matches, and 4 points in their last two matches. That would give them 7 points, which generally isn't enough advance from the group stage. (The sum of the expected points is 7.37 points.)
The most likely road to 10 points for the Sounders would probably have been a win at Honduras, a draw at home with Monterrey, and then wins in the last two games.
All of this makes me wonder a bit if the order of the group stage games makes much of a difference in these things. If the schedule went in reverse, it's not that hard to imagine the Sounders starting strong out of the gates with two wins. Then maybe by the time they got to the home game vs. Monterrey, Monterrey would have had essentially secured a spot in the next round and not really brought their A team to Seattle for the 5th game. And even if it was close going into that last game, they'd likely only need to keep the game close and hope to do well on goal differential, rather than hoping to pull themselves out of a goal differential hole.
Looking back at this, I think I probably had rather naive expectations for the CCL. I figured that the Sounders could do better than MLS teams had in the past just by taking the tournament "more seriously," but on the whole over the last 1.5+ seasons, the Sounders have only been upper mid-table and not really the class of MLS in performance. Then they got drawn into a rather difficult group and it looks like they needed at least a point out of Honduras pretty badly, and they weren't able to get it.
I sure hope we get another crack at this next year.