# NBA’s Plus/Minus Rating System

If you have ever checked out an NBA box score on ESPN.com, for example, you’ve likely noticed at the far right just before PTS, a column that reads “+/-“.   If you did notice it and bothered to mull it over, it didn’t take you long to deduce that the number attributed to each player in that box score was the cumulative score differential while that player was on the floor in that game.

So, in simple terms, if a player was in the game for its last 6 minutes and his team outscored the opponent by five points, his +/- would be +5.  On the more complicated side, if a player played 38 minutes in 4 different shifts, the net total might be the same +5, but the shifts may have individually netted +10, -6, +1 and 0- still, a pretty simple concept to digest.

Like any other stat, plus/minus is merely a tool to help analyze performance.  While any stat is not the answer to all our problems, over a large sample size Plus/Minus can aid coaches in quantifying what they might already surmise by observation alone.

Let’s examine some of the plusses:

• It can account for all the hidden contributions that players make- like deflections, fouls drawn, charges taken, second assists, help and recovers, good spacing etc.
• It can help a coach determine which player combinations work the best.  “Chemistry” is difficult to compute but Plus/Minus can be helpful in this assessment.
• If one needs another metric to justify playing time or a lack of, this tool can be powerful.
• If desired, it can be a one-stop-shop method of analysis since it really includes every aspect of play.
• It might dawn on certain players that the only thing that matters is how the team performs statistically when they are on the floor.  It might help accountability.

Let’s also look at some of the possible issues:

• As mentioned, one needs a number of games for the stat to be most meaningful.  One game can be an anomaly.
• Obviously, it greatly depends on with whom a player is on the floor.  I’d love to be the 3rd, 4th or 5th player on the floor with Steph Curry and Klay Thompson.  On the flip side, there are players that I’d like to avoid-for this stat’s purpose.
• The system requires a responsible, dedicated charter.  The number of subs one uses and the frequency of substitution makes charting even more rigorous.
• If you’re already fairly analytical, one might not want to add another method to over-complicate matters.

Like any other decision coaches make to add to or delete from their programs, having a working knowledge and understanding of the Plus/Minus system is valuable in and of itself, whether one decides to adopt it or not.

Originally posted 2015-12-03 18:18:56.