Two economists, Joseph Price and Justin Wolfers, found that white N.B.A. referees disproportionally call fouls on black players, while black refs call more fouls on white players. “These biases are sufficiently large that they affect the outcome of an appreciable number of games,” Price and Wolfers wrote....except that's not what Price and Wolfers found. The paper is here. Look particularly at Table 3. What it shows is the racial composition of refereeing crews had almost no effect on the foul rate of black players. On the other hand, having a higher proportion of black referees tended to increase the number of fouls called on white players. White players had more fouls called on them overall.
Whether the racism was positive (white refs calling fewer fouls on white players) or negative (black refs calling more fouls on white players) is impossible to disentangle from the data, since a foul call is inevitably subjective, and it's clear white and black players tend to segregate somewhat by position and role.
But either way, the treatment of black players did not depend significantly on the race of the officiating crew. Or to quote the authors themselves:
This analysis reveals that the bias we document primarily affects white players.2 This is a departure from more standard accounts of discrimination which involve whites actively discriminating against blacks, although our setting is unusual in that black players are the majority group. In turn, this may reflect either white players being favored by white referees or disfavored by black referees, although our identification strategy (which relies on random assignment of refereeing crews) does not allow us to sort out which group of referees is responsible for this bias.This directly contradicts Kristof.