Friends don’t let friends go isolation


Click for a full-sized, interactive version

In my never-ending crusade to convince people that isolation and heroball are generally terrible ideas, I present to you the above chart. On the y-axis is the percentage of a team’s offensive plays that are isolation plays. On the x-axis is the change in offensive efficiency (points per possession) between a team’s isolation plays and all other plays. All data are from Synergy.

Let me explain that last bit a little more. My criticism of iso ball isn’t that it’s bad, but that it’s inefficient compared to other offensive sets. Thus, the nominal efficiency of a team’s isolation plays is much less important than the efficiency of those plays relative to the efficiency other plays. In other words, if a team didn’t iso, what would the difference in efficiency be?

Take this example. Team A’s average offensive efficiency is 150 points per possession (PPP). Its offensive efficiency in iso plays is 100 PPP. Team B’s average offensive efficiency is 100 PPP. Its offensive efficiency in iso plays is 99 PPP. While Team A is technically better in isolation sets than Team B (100 is bigger than 99), it is losing more by isolating than Team B. By going iso, Team A is giving up 50 PPP (150 minus 100, or 33% of its previous efficiency) whereas Team B is only losing 1 PPP (100 minus 99, or 1% of its previous efficiency).

This is why the x-axis represents change in offensive efficiency. It’s the opportunity cost a team incurs by going to an iso set, which is much more important than how good a team is at isolating in general. Basically, think of isolation plays as a trade off, as opposed to a vacuum.

OK, onto the chart. The first thing you should notice is that no team sees an increase in offensive efficiency by going iso. I want to repeat that. When every team goes iso, it has a less likely chance of scoring. If that doesn’t convince you that isolating is not a particularly good idea, then I don’t know what will.

That being said, some teams suffer a lot less from going iso than others. The Clippers, for instance, only see a 2% decrease in offensive efficiency. The Bulls, on the other hand, see a 25% decrease in offensive efficiency by going iso. This makes sense, given the composition of the two teams. Interestingly, both these teams are less likely to rely on isolation sets than the league average.

The lower left quadrant is comprised of teams who have a lot to lose by isolating, but don’t do it very often. These teams are smart. They know that they trade off a lot by going to iso sets, so they do it very infrequently, maybe just at the end of the shot clock or something. The aforementioned Bulls, at 6%, are actually the fourth lowest team in terms of isolation plays as a percent of all offensive plays. Very wise.

The upper right quadrant is comprised of teams who are who lose less with isolation, and do it more frequently than other teams. These teams have some combination of really good 1-on-1 players and really bad other options, such that even though going iso is less efficient than other options, it’s probably not the worst option. Leading the charge in this group of teams is the Thunder (screw you, Kevin Durant!). Also nodding his head vigorously is Carmelo Anthony, whose team is by far and away the most iso-happy team in the league, but actually suffers less than you might think from those iso sets.

Then there’s the upper left quadrant. This is comprised of teams who lose a lot by going iso, but still do it more frequently than other teams. The big outlier in this quadrant is, unfortunately, the Houston Rockets. And it’s not that close. Most other teams in this quadrant are at least hugging one of the average lines. The Rockets are pretty far away from both. They isolate on over 10% of their offensive possessions (5th most in the league), but suffer an almost 20% drop in offensive efficiency every time they do (3rd worst in the league).

I understand that, in certain situations, isolation sets are unavoidable, such as at the end of the shot clock. But given how much the Rockets have to lose by going iso, one would think they would do everything in their power to avoid those situations. Also, teams don’t become 5th best in the league at something just by pure chance. Some of those iso sets are by design. The data says those designs need to be changed. Seriously, I bet the % of end-of-quarter possessions that end in isolation is over 80%, usually for Harden or Lin. WHHYYYYYY!!!

In conclusion–Just. Say. No.

About the author: Richard Li is an independent researcher and consultant. He likes numbers and pictures.

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