Why You Can’t Always Trust Plus/Minus

Our team is now 15 games into the season, and with that many games played it is a great opportunity to evaluate playing time and lineup combos. As I was noodling around, I discovered some lineup combinations with a great plus/minus, and a mediocre net points-per-possession (Net PPP). Here’s the example:

When we substitute, there’s a significant amount of “offense/defense” logic determining who to play at any given instant. If we have possession, a better shooter will often be inserted. Likewise, if the other team has possession, we will substitute a better defender.

This pattern skews the plus/minus, as a player or lineup combo will eventually have more offensive or defensive possessions. A player or lineup with more defensive possessions will have a lower plus/minus, and one with more offensive possessions will have a higher one. The example above highlights one lineup, with a great plus/minus, and a low net PPP. With 17 more offensive (59) against defensive possessions (42), that lineup will show a greater plus/minus, yet overall it’s just about average.

If you’re using HUDL, Synergy, or another one of our competitors, and are relying on their plus/minus (even time-adjusted plus/minus) to make decisions, you may be missing the true story. Especially if you’re strategic about the timing of your substitutions.

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Category: Analytics