One of the attributes that is often attached to defensemen is the ability to clear rebounds. You hear this quite often on NHL broadcasts, usually after a flurry of rebound shots that ultimately wind up in a goal. The colour commentator will jump in and imagine the goalie is saying to his defensemen, “I’ll stop the first three, you get the fourth one.”

But just how much is there to defensemen’s ability to prevent rebound shots?



Back in December, our own Matt Cane wrote about how well defensemen are able to control play in the defensive zone and prevent follow-up shot attempts after an initial shot attempt. Matt’s analysis showed that Luca Sbisa was more that two standard deviations outside the NHL norm when it comes to allowing follow-up shot attempts:

That would make Sbisa worse than 95% of all NHL defensemen. And if I were to apply the eye test to that chart, I would probably say that he’s actually more like three standard deviations outside the mean, making him worse than 99% of all NHL defensemen at preventing follow-up shot attempts.

Given these results, you can imagine my surprise when I heard Canucks’ GM Jim Benning say this following Sbisa’s return to the lineup just before the All-Star break:

And if there was a rebound, I think having Luca [Sbisa] back in the game helped us around the net, being physical and taking their guys out from getting second and third opportunities to score.

Now, to be fair, Matt’s analysis focused on shot attempts, rather than strictly rebound shots. A shot attempt that misses the net and bounces into the corner is a lot less dangerous than a save that leaves a puck lying in the slot. You would also expect a defenseman to be more responsible for controlling rebound shots than retrieving pucks away from the slot and preventing additional shot attempts. At that point, the responsibility has to be shared among all five skaters on the ice. Maybe Benning’s eyes are able to cut through all of that extraneous noise and focus in on the loose pucks that really matter.

So let’s put Benning’s eye test to the test.

I asked Matt to help me out with the data collection on this, and he was able to provide raw shot counts for all Canucks’ defensemen for the 2014-15 season and for the 2015-16 season through to just before the All-Star break:

Here “rebounds” refers to all shots on goal that did not result in an immediate stoppage in play, i.e. weren’t covered by the goalie or deflected out of play. Think of them as loose pucks following a save. “Rebound shots” are then shots that occur within two seconds following the initial save. Some analysts count any shot within three seconds of another as a rebound, but for our purposes two seconds is more likely to better correlate with shots that are closer to the net and thus within a defenseman’s ability to control.

Presumably, it is rebound shots that Benning is referring to when he speaks of Sbisa’s abilities to prevent “second and third opportunities to score.” Looking at the raw data, Sbisa has actually allowed the most rebound shots on the team over the last season and a half, but we know that’s going to be skewed by a number of factors including ice time and how well the goalie is able to control the number of rebounds given up.

Let’s address those factors one at a time. First let’s look at rebound shots allowed on a rate basis:

The good news is, he’s no longer at the top of the list. The bad news is, out of the defensemen that actually still play for the Canucks, he’s in a statistical tie for first.

There are two things to note here. Well, three things. First, Kevin Bieksa…oof. Second, Sbisa and Bartkowski allow the most rebound opportunities of current Canucks defensemen. And third, even though they are the worst among the Canucks, Sbisa and Bartkowski still only allow 1.4 rebound shots per 60 minutes of 5v5 ice time. If they’re playing about 15 minutes per game at 5v5, that’s only 0.35 rebound shots per game. Now, I’ve never played the game, but why do important people think this is such a valuable skill?

Anyway, let’s move on. What about the goalie’s role in all this? After all, they have some responsibility in controlling rebounds and stopping play.

Back in November, Matt took a look at rebound control and found that, on average, about 29% of saves are followed by a stoppage in play. By this measure, Canucks goalies have been slightly above average over the last year and a half, stopping play 32.5% of the time:

But when Sbisa is on the ice, they actually give up about 2.4% more rebounds than their average. One reason could be that, as you can see in the image up top, he’s quite adept at screening his own goaltender, giving him less time to get set for a shot and thus being less prepared to freeze it or otherwise direct it out of play.

So we know that Canucks’ goaltenders give up slightly more rebounds with Sbisa on the ice, but how well is Sbisa able to prevent those second and third opportunities that Benning is so focused on?

Again, Kevin Bieksa leading the way. But Sbisa, Bartkwoski, Hutton and Weber not too far behind. Among active defensemen, Sbisa is definitely not better than anyone else at preventing second and third chance opportunities. In fact, he is statistically in a dead heat for worst on the team. Here it is graphically:

The farther you are above the line, the worse you are at suppressing rebound shots relative to the Canucks defensive corps as a whole. Bieksa was in a class of his own last year, but Sbisa (and Weber) aren’t far behind during their time with the Canucks. I should note that Alex Biega, for all his faults, might actually be the defenseman that Benning thinks Sbisa is.

But back to the topic at hand: I’m not sure what Benning thinks he’s seeing, but if he really thinks Sbisa helps his team prevent rebound shots, the only eye test he should be taking advantage of is the kind you get from an optometrist.

We’ve shown that Benning is not actually seeing whatever it is he thinks he’s seeing, and even if he was, it’s really not that important in the overall scheme of things. After all, allowing 0.35 rebound shots per game is only worth about 0.1 goals per game, or 8 goals over an entire season. Not insignificant, but remember that’s an absolute number and, in fact, is probably what we should consider replacement level.

But what if clearing rebounds was important. Is it even what we could call a skill, i.e. is it repeatable? The answer appears to be no.

Looking at all defensemen that were on the ice for at least 200 saves in both 2013-14 and 2014-15, we can compare their rebound shot % from one year to the next. If rebound prevention was a repeatable skill, we would expect to see some correlation in year-to-year performance.

However, that does not appear to be the case.

Even if we go back to 2009 and look at the correlation between one year and the next for each defenseman that was on the ice for at least 200 saves, we still do not find anything meaningful even over the larger sample size:

In fact, the correlation is even worse than before and performance on this metric is essentially random from one year to the next.

Finally, since I have the data set, here is the year-to-year correlation between 2013-2014 and 2014-2015 on rebound control for goaltenders:

So in contrast to defensemen’s ability to suppress rebound shots, which we’ve seen is essentially non-existent, we can see that goalies’ ability to control the number of rebounds generated is in fact repeatable, verifying what Matt Cane has shown previously.

Conclusions

Based on the preceding analyses, we can conclude that:

(Some) NHL GMs think they’re seeing things that they aren’t really seeing. In the overall scheme of things, suppressing rebound opportunities doesn’t really have much of an impact over the course of an entire season. Even if it was important, there’s no indication that this is a repeatable skill for defensemen. Goalies do have some ability to control the number of rebound opportunities generated off of shots on goal.

Thanks again to Matt Cane for help compiling the data. Follow @Cane_Matt

You can find me on Twitter @petbugs13. Follow @petbugs13