Tom Meagher has an excellent article at The Hardball Times breaking down the cause of home field advantage in MLB. The results are quite shocking. The home/away difference in balls and strikes explains about two-thirds of home field advantage. Why is this?
Are umpires really helping out the home team? Are pitchers more familiar with the pitching mounds at home? Are visiting batters having a harder time seeing the ball or reacting to it? Is fatigue affecting the results?
It may be significant here that the total number of balls in play (bip) per plate appearance (pa) does not differ much the home/road factor for bip/pa was 1.0079 in the NL and 1.0002 in the AL. That leads me to believe that the major change in walks versus strikeouts is related to judgment of whether a pitch is a ball or strike either the batters poor judgment, induced by lack of familiarity with the hitters backdrop, or the umpires judgment, giving better calls to the home team.
Interesting stuff here. I expect there is more to come.