It's a familiar complaint: Your team goes on the road for a big game, and gets totally jobbed by the refs. But do away teams really get fewer calls?
Over on his blog Visual Statistix, Seth Kadish took a look at fouls/free throw attempts, penalty calls, strikeouts/walks, and penalty minutes for the last three NBA, MLB, and NHL regular seasons (last four for the NFL). As you can see on his chart above, each of the leagues sees the home team get an advantage. The consistency between sports is striking: Kadish found that away teams got 3.1 percent more penalties in the NFL, 4.0 percent more foul calls in the NBA, 4.3 percent more penalty minutes in the NHL, and 4.7 percent more walk calls in MLB. This isn't necessarily on the refs (although there is robust evidence that refs are psychologically influenced by home crowds); it's possible that the players themselves are being influenced by crowds or travel, although books like Sportscasting have refuted these theories to some degree.
Regardless of root cause, it's clear that there's a real home/away gap in total officiating numbers, and this gap is likely large enough to make up a significant chunk of what we consider general "home field advantage." Home teams win 53.9 percent of their games in MLB, 55.7 percent in the NHL, 57.3 percent in the NFL, and 60.5 percent in the NBA—that's not an enormous advantage, and certainly one that can be nudged by a few key calls.