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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You say that we need to differentiate between certain kinds of steals to have a conclusive say on wether steals are bad or good for a defensive. But that is not the point, steals are never bad, because a steal means you actually got the ball. That never hurts a team, gambling WITHOUT getting the steal is what hurts teams. So if we had a stat that would count steal attempts and we would build a percentage out of the steal attempts and the successfull steals (kind of like fg%), we would see that people with low steal% but high numbers in steal attempts hurt the defense just like high volume shooters with low fg% hurt their offense. So applying high pressure and creating a turnover and a steal is the equivalent to an inside shot while straying from your man to gamble the passing lanes is a three launched with a hand in your face. One thing is efficient and will help you win, the other will not.
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i agree, you cannot analyze how much steals help without seeing if possessions beginning with a steal are more likely to generate points.
Jon, I am not sure I follow your interpretation of the results. As I understand your numbers, an increase of 1% in steal rate yields an increase (decrease?) in DE of -.93 or -.82. League-wide, DE this year according to B-R.com is 106.8. A 1% decrease in this is -1.07. If I am not mistaken, what your numbers show is that increasing steals has a less than proportionate effect on defensive efficiency. In turn implying that going for steals has adverse defensive consequences.
However, this, of course, is not the complete picture. There should be big gains on the offensive side where open court steals disproportionately yield high return fast breaks. Regressing steal rate on OE will be necessary to complete the story.
schtevie,
I think you’re missing the point of the article. I was not looking for a proportional decrease in defensive efficiency. What I was looking for was any decrease in defensive efficiency at all. The point was to see if steals are good or bad. If they’re good, the slope is negative, and if they’re bad, the slope is positive. How “good” they are was not really the focus of this article, although it certainly could be something to look at going forward. The same goes for the correlation between steals and offensive efficiency.
-Jon
Jon, has anyone ever alleged that steals are bad? The first order effect is, by definition, positive and large: a steal precludes a scoring attempt on that possession. The only controversy I am aware of is the degree to which the second order gambling costs (suggested to be 0.14 to 0.25 by your numbers) outweigh the offensive fast break gains. I expect that the answer, provided by the symmetric regression of steal rate on OR, will be a clear ‘no’.
schtevie,
It was a question proposed to me by someone, and I don’t think it’s crazy to question if steals really are good. Obviously a steal is a good thing because it causes a turnover, but theoretically more steal conversions could be accompanied by more failed steal attempts. If there were enough failed attempts, they could outweigh the benefits of causing turnovers. The data shows that’s not the case, but I don’t think it’s unreasonable to investigate.
In addition, many fans complain that some of the best defenders as decided by the all-defensive teams are often overrated because of box score stats such as steals, so it’s worth looking at.
-Jon
There’s nothing to worry about.
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