Plus-minus (+/-)

Plus-minus tracks the score differential accumulated while a specific player is actively playing: for every point or goal the player's team scores while they are on the field, court or ice, plus-minus goes up by one; for every point or goal conceded, it goes down. It is one of the oldest whole-game impact stats, long used in hockey and later adopted by basketball.

Raw plus-minus is simple to calculate but confounds a player's own contribution with the quality of every teammate and opponent sharing the field at the same time, so a strong player surrounded by weak teammates can post a worse number than a weak player who happens to share the floor with stars. Adjusted and regularized adjusted plus-minus models try to isolate individual contribution using regression across thousands of lineup combinations, and basketball's box plus-minus estimates a similar quantity from box-score stats instead of lineup data.

Analysts still cite raw plus-minus for a quick read on lineups and on/off splits, but treat single-season or single-game values with caution because of small-sample noise; a player can post a wildly positive or negative plus-minus over a short stretch purely from teammates' shooting variance. In hockey, shot-attempt versions such as corsi and fenwick were developed partly because goal-based plus-minus samples are too small and too slow-scoring to be reliable over a season.