Creating turnovers on the defensive end certainly is a good thing. After all, it is one of the Four Factors. Still, the ability of a defense to generate steals in particular is not always assumed to be beneficial. Perhaps it is better to play more safe and solid D. I’ve decided to look at the numbers and see what conclusions we can draw.
Using play-by-play data, I calculated the Steal Rate (the percentage of opponents’ possessions that ended in a steal by the team in question) for each lineup that appeared in at least 400 possessions last season. I then compared that lineup’s Steal Rate to its Defensive Rating (points allowed per 100 possessions) and plotted the results in the chart below. If steals are important, a higher steal rate should lead to a lower Defensive Rating, and therefore a negative slope:
So far, it appears as though steals are important. Despite a low r-squared, these results certainly are meaningful and are very much statistically significant. We can’t say that the number of steals entirely explains how well a defense will do (as evidenced by the low r-squared), but we can say that there is a correlation between high steal rates and low Defensive Ratings.
But we should pause for a second. This graph can be very misleading. Perhaps there are some confounding variables (hidden factors) that make the results appear to be this way when they really shouldn’t be. In other words, maybe good defensive teams just have more athletic players in general. This may cause them to get more steals, but it doesn’t mean steals are the reason they’re better. If a bad team were to go for more steals, they’d still be a bad team and have a poor Defensive Rating.
However, there is another approach that we can take. For each lineup, I’ve calculated the projected Defensive Rating based on the individual Defensive Ratings of each player in the lineup. I then calculated the difference between the lineup’s projected Defensive Rating and actual Defensive Rating. This difference was regressed against the lineup’s Steal Rate.
What is the point of this? This method attempts to zoom in on just steals. By taking a lineup’s projected Defensive Rating into account, we’re trying to adjust for other confounding variables. This way, if there is a negative correlation between the difference and steals, it is further evidence that steals are important. A negative slope in the graph below indicates that steals are important:
Again we see more evidence suggesting that going for steals is generally beneficial. The r-squared is low but the results are statistically significant.
Of course, these graphs don’t specify what types of steals are good. Risky attempts may very well hurt the defense.
In conclusion, based on the evidence I’ve presented today, I would suggest that lineups (and, theoretically, players) that record more steals are often better on defense. To some, this may be obvious, but to others it may not be. We can never know for sure how important steals really are, but the stats think they matter.
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