Have you ever wondered if past penalty calls impact the next call in a game?  What about those times when your team gets three power plays in a row and everyone in the building knows they’ll get the next penalty?

Noah Davis (@noahedavis) and Michael Lopez (@statsbylopez) took a look at just that for fivethirtyeight.com:

fivethirtyeight - Penalty ChartThis is pretty compelling evidence that referees’ past calls influence their next calls. […] The tendency for prior violations to affect NHL penalties is enormous; when home teams are owed penalties, they are called for penalties at much lower rates, and the inverse holds for away teams.

The effect is even more pronounced when a string of penalties against the same team starts a game. If a game starts with four straight penalties against the away team, for example, the home team is about three times as likely to be called for the next one.

“In the overall complexion of the game, it gives the team that has committed multiple infractions recognition that if they commit the crime, they’ll do the time,” says retired NHL referee Kerry Fraser. “On the other hand, they know the ref is fair because he called a penalty against the other team when he saw it. It doesn’t cause further frustration for the team that is taking more of the penalties.”

There’s even more of an impact in the postseason

In playoff games, the referees’ balancing effect grows even stronger. Our hypothesis: referees are trying to even out playoff games, where the pressure is on for the officials to avoid becoming a storyline. When the home team is owed a penalty in the playoffs, the frequency of calls on the visiting team is significantly higher than it is during the regular season. (If the away team is owed a penalty or penalties, the effect is about the same as it is during the regular season.)

Overtime produces the most dramatic results, with the second penalty call of the extra period about three times as likely to be whistled on the team that received the first power play.

The score, though, doesn’t seem to matter.

[O]ne factor that does not seem to account for the tendency of past calls to affect future ones is the game’s score: The shape of home-team penalty frequencies is the same as on the chart above, no matter the score.

Read the full story over at fivethirtyeight.com.