I found a few studies regarding referee bias, and it is a real phenomenon. From what I gathered, home field and crowd noise plays a big part, as well as the [subconscious?] tendency to want to “even things out”.
Abstract: Results of the analysis indicate that officials are more likely to call fouls on the team with the fewest fouls, making it likely that the number of fouls will tend to even out during the game. This increased probability increases as the foul differential increases. In addition, there is a significant bias toward officials calling more fouls on the visiting team, and a bias toward foul calls on the team that is leading in score. The result is that the probability of the next foul being called on the visiting team can reach as high as .70 during some game circumstances. Finally, implications of this officiating bias are explored, including the fact that basketball teams have an incentive to play more aggressively, leading to more physical play over time.
Statistical models show referees are homers – Research indicates officials unwittingly favour home teams and are particularly swayed by large crowds
Here’s an interesting one about Omission Bias. Check out the NBA rate of calls throughout the game, and how they diminish for more subjective calls from the first half to the 4th Q and especially OT when it’s pretty clear that the refs “let them play”.
All in all, I think there are psychological factors at work, including the theory that a team that’s perceived to be “not as good” won’t get the calls it needs to upset the better team. That’s the real Catch-22. I also think that individual refs are biased against certain teams – whether it’s conscious or subconscious is another matter.