In the first round of the playoffs, the Boston Celtics are uncharacteristically struggling with the New York Knicks. There are a number of different reasons why the Celtics are struggling, but the most glaring one is the number of offensive rebounds that the Knicks are grabbing so far in this series.
In the first two games of the series in Boston, the Knicks have grabbed 33 offensive rebounds, or 36.7 percent of the total offensive rebounding opportunities (according to Synergy Sports Technology). This means that the Celtics are grabbing the defensive rebound just 63.3 percent of the time. This is a significant drop-off from the regular season. Over the course of the year, Boston rebounded 74.7 percent of available misses. This means that the Celtics are grabbing 10 percent fewer defensive rebounds in this series than they are used to.
So why are the Knicks grabbing so many offensive rebounds? It is the same reason why they seem to be scoring easier than expected (though they are not scoring at their normal rate, they do seem to be scoring more/easier than I would have expected against the Celtics' tough defense). The rotations on the Boston efense have been a little off during the first two games of the series. Not only does this hurt their ability to contest shots, but it also makes it harder to grab defensive rebounds that don't bounce straight to them:
What is usually so great about the Celtics' defense is that they trust each other so much and they know where each other are going to be at all times. I say usually because that hasn't been happening too much during their series with the Knicks. On the above play, Rajon Rondo tries to pass Anthony Carter to Jeff Green as he leaves him to double Amar'e Stoudemire, but Green never picks him up, in part because nobody rotates down to help him with Jared Jeffries. Stuck trying to keep two players off of the glass, Green makes the logical decision to box out the bigger guy, but this leaves Carter for the easy tap-in.
Normally, these rotations are happening so quickly that there is usually never an open offensive player, but in this case Paul Pierce never rotates down. He tries to after the ball goes up in the air, but he doesn't get to Carter in time.
On this play, you have a four-on-two fast break by New York, with Carmelo Anthony trailing the play as the third man in. The Knicks being the Knicks, they get up a three-point shot in transition, and as the ball is in the air Carmelo gets in the paint. Instead of rotating over to box him out, all three Celtics in the paint run straight towards the rim. The ball comes off long and bounces right in Anthony's hands for the putback.
Here, Rondo gets beat by Chauncey Billups, and instead of providing help Pierce is caught watching Anthony with his back turned towards the basketball. With Pierce unable to provide help, Jermaine O'Neal is forced to range over to try and block the shot. He is unable to and as the shot comes off of the rim, O'Neal's man (Ronny Turiaf) is able to grab the offensive rebound.
Finally here, the Knicks are using a dribble handoff offense and eventually Shawne Williams gets the basketball and takes a jumper at the top of the key. As the shot is in the air, you see the two Knicks on the block with inside position on the Celtics. This inside position is due to poor rotation and New York is able to take advantage by grabbing the offensive rebound.
Grabbing the defensive rebound is very important to the Celtics in this series for two reasons. First, when they grab the rebound, they stop the Knicks' offensive possession. By giving up the offensive rebound, they are giving a high-octane offense another possession and 24 more seconds to work with.
In addition, the Celtics seem to want to get Rondo in the open court during this series. While they can do this off of makes, it is much more effective if Rondo gets the ball on the run off of a defensive rebound. By giving up offensive rebounds to the Knicks, they are not only hurting their defense, but their offense as well.
Sebastian Pruiti is an author of Basketball Prospectus.
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