Officiating is a piece. So is "friendly confines", especially in football and baseball. The Lions success at home this year is probably in part thanks to the fans, but also being in a dome with a team and QB that does better inside. In baseball, your outfielders learn the ins and outs of that field like the back of their hand over 81 games. To a lesser degree, your pitchers know what they can get away with up in the zone too.