Referees can be inconsistent. There have been flagrant calls lately on Carmelo Anthony and Russell Westbrook, while there was an in-game non-flagrant call on Greg Monroe (Upgraded to Flagrant 1 by the NBA). But research also suggests they are biased.
According to Scorecasting: The Hidden Influences Behind How Sports Are Played and Games Are Wonby Moskowitz and Wertheim, social approval from the home crowd impacts referee calls. In their paper, Price, Remer, and Stone found that referees call turnovers in favor of home teams, teams losing during games, and teams losing in playoff series.
Star players also get more free throws than regular players during the final minutes of the game. Caudill, Mixon, and Wallace studied the 2011 NBA Playoffs and found that star players get an additional 0.32 free throw attempts per minute during the fourth quarter.
Some of this is apparent to NBA fans who have long criticized unfair calls by referees. Fans point to examples like the Lakers against the Sacramento Kings in the 2002 finals, and scandals such as the NBA’s “Tim Donaghy” scandal. So are referees doing this on purpose?
The research isn’t certain.
An important thing to consider is that these biases are implicit in nature and have little if any correlation to explicit bias. Meaning that the biases are caused by natural social-psychological factors, like social approval, and the referees are not deliberately trying to influence the game.
For its part, the NBA does have rules in place to prevent bias. According to the NBA, the referees work 70-75 games a year, and are chosen randomly with no thought given to the teams competing. The referees are not allowed to officiate more than nine games for any team over the season or twice in a city within fourteen days.
Intentional or not, however, natural biases do exist. NBA refereeing will always involve human error, but there are certain situations that should require specific reform. In the most critical of moments for NBA games, these changes could decide winners and losers.