Almost everyone picking Portland seems to cite home field as the reason, tacitly or explicitly acknowledging that the game is otherwise a toss-up (and that maybe NYCFC is in fact better). Given MLS HFA, it's not irrational to pick a lesser team at home.
Which leads me to this article:
Short answer? They don't win. Or at least not enough. This has been discussed ad nauseum on the interwebs for a while, but the MLS home field advantage is the strongest of any of the five major professional sports in the US. Not only that, it is considered one of the strongest home field adva
www.americansocceranalysis.com
MLS Away teams win 25% of the time. In trying to figure out what underlying factor sets the Away wns apart from all the Away losses (and after moving past the obvious and not very insightful truth that Home teams tend to score more goals), he considers and rejects a lot of possibilities. The distinguishing factor is
NOT:
- more shots
- more shots on goal
- creating more expected goals
- outperforming your expected goals (ie finishing better)
Instead, the difference maker seems to be getting, on average, better high probability shots, regardless of how many. Away teams win when their average (or median) xG per shot is higher than the Home team. He finds this holds even when the Home team takes a lot of shots and accumulates higher xG than the Away team. The best road teams in MLS this year were New England, the Sounders, and Colorado. This stat holds for all of them. Basically, on the road, the key is, get some very high quality opportunities to pull up your xG per shot average, and don't allow the same for the Home team. But you can let the home guys shoot and shoot if they're doing so to accumulate a lot of low probability shots from distance, or with defenders nearby, and not in transition, etc.
I'm not 100% sold on causality here as opposed to just correlation, but it's an interesting read and the author really lays out his data and reasoning. It would probably feel more satisfying and easier to implement a strategy if the answer had been more SOGs or more xGs. Getting a higher average xG regardless of totals seems kind of indirect, though it does suggest some areas of focus for both offense and, I think, especially defense. Finally, in any given single game, eg MLS Cup, the tendencies and usually-this-happens factors can all get thrown out the window.