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Do NBA Referees Favor Home Teams?
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Do NBA Referees Favor Home Teams?

Many NBA fans think NBA referees are probably biased at some degree. This bias can be towards larger market-teams, towards teams with superstars or towards home teams. But in reality there is hardly statistical evidence that referees really favor some teams or players.

 

In this analysis, we tried to use a new approach to observe if there is a referee bias towards home teams and if the number of attendance is really important for referees’ decisions. To do so, we collected all the play-by-play data of 2014-15 regular season and looked at traveling violations, shot clock violations, offensive and defensive 3 seconds violations, 5 seconds violations, flagrant 1, flagrant 2 and technical fouls, and lastly offensive fouls. These are the stats directly related to referees behavior.

 

Afterwards, we compared these statistics of all NBA teams for both in their home and road games. For instance, we compared average traveling violations of Chicago Bulls and their opponents in United Center games and took the difference; then did the same thing while Chicago Bulls are at road games. Finally, we calculated the difference of both. Thereby, what we reached is how many more traveling violations on average per game that Chicago Bulls performed than their opponents at road games comparing its home games. We believe higher values means higher referee bias towards home teams.

 

Let’s look at the results now. The following table summarizes the average of this bias according to all teams’ values. Clearly, for some of them we can state referee bias. Those stats are traveling violation, offensive 3 seconds violation, technical foul and offensive foul. For these 4 items, home teams are hearing less referee whistles. On the other hand, for shot clock violation, defensive 3 seconds violation, 5 seconds violation, and flagrant 1 and 2 fouls, it seems there is no referee favor towards home teams.

 

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The below table gives us team based details for biased stats. The green values signify that on average, teams got less calls then their opponents at home comparing at road. The red ones are exactly opposite.

 

There are 8 teams which got comparingly less calls at home with all these 4 stats: Celtics, Bulls, Pacers, Heat, Magic, Kings, Raptors Jazz. But only one team, Milwaukee Bucks, got no advantage for all these stats at home.

 

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As for the attendance, we couldn’t find any significant impact of it. There is no statistically significant distinction between teams for our stats when the attendance is high or low. Even there is no significant correlation between them. Thus, we can say that for NBA, home court advantage is not about how many people are there. But just a not here, last season’s lowest attendance was 10079 (NYK at PHO), which is in fact not low at all. For who wonders, the highest attendance was 22879 (CLE at CHI).

 

 

3 Comments

7
  • Gale Bertram

    It’s about what they don’t call.

  • Shane

    I don’t understand why you’d suggest defensive fouls aren’t “directly related to referees behavior.”, they’re as judgement oriented as any (and therefore I’d think reasonable to think more likely to be biased, than something like 3 or 5 seconds). The fact that there is such a range and inconsistency of values team to team suggests to me that most of your results are probably noise, except for perhaps a very slight overall home bias, which would be better shown without breaking it down (though almost every paper\writeup I find seems more interested in such). While it’s possible a bias could be hidden more carefully by giving unimportant calls more often to the road team or in certain games, it’d be a rather complex subconscious\conspiracy to imagine at that point…

    • Gürhan Günday

      Unlike the mentioned stats in the analysis, I believe defensive fouls reason can’t be quantified and measured without personal perception. The number of defensive fouls committed can also be analyzed in the same way, but I think it can’t be reliable.
      This post brings a different approach on this debate, though we did not suggest or find any hard evidence towards referee bias.

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