Graphing a team’s blocks per 100 possessions against their defensive rating paints a revealing picture. You can see from worst to best defensive efficiency that block rate varies at a high rate. There is little to no correlation between blocks and defensive efficiency(1). This may come as a surprise, but I will discuss further why blocks are not good at indicating how good a team or player defends.
For one, blocks are highly unlikely to occur in any given possession. This season, only 5.3% of field goals attempts were blocked. Due to the low volume of blocks, a teams defense cannot solely rely on blocking many shots to carry a defense. The player with the highest block percentage(2), Jaren Jackson Jr. at 7.4%, still falls below the rate where just his blocks make Memphis’ defense as good as it is. The threat of blocks or a good contest is more important than the block itself.
Use the above play as an example. Instead of inviting the player into a shot, Gobert deters the player from ever shooting the ball using his positioning. He keeps Green out of the restricted area and Green does not want to take a contested shot against Gobert. If a player does not attempt a shot then naturally they have a 0% chance of getting the ball in the basket. This indicates that good positioning rather than timing blocks creates more opportunities for defenses to succeed.
Since blocks are most likely to come near the rim and inviting a player in closer and closer has adverse effects for the defense, it can be seen how defenses that allow lots of blocks can still be bad defenses overall. In the 2022 regular season, a shot within six feet of the basket had a 61.3% chance of going in. Just four more feet out at the distances between six feet and ten feet the percentage lowers all the way to 40.3%. Even when the top ten rim protectors(3) are the ones contesting the shot near the basket, there is only a 50.3% chance the shot will go in.
Blocks are not useless, however. While they may not indicate good team defense, they are tools to be used in certain situations. Generally, blocks are used as saves from defense breakdowns. Since blocks mostly happen within or near the restricted area, the initial defense must lead to a player getting within this range before the block attempt. Letting a lot of players to get within this range is a recipe for a bad defense(4).
In the above play, the perimeter defender is easily beat by the ballhandler. Vanderbilt sniffs out the play early(5) and positions himself in front of the hoop to save the layup. The block saves the contested shot from going in.
A help defender coming from the weak-side to contest a defensive breakdown is a common save deployed by a defense. In this example, Robert Williams sees Huerter get past his man and closes in to stop the easy lay-up(6).
In this play, the ballhandler has a mismatch and takes the defender to the rim to get an easy shot. Mobley sees this and follows the play down to the rim to get an arm up when Giddey shoots. This leads Mobley’s man to get the offensive rebound due to Mobley jumping away from the hoop to block the shot. You may have noticed that with each play showcased that the ball returned to the team who gets their shot blocked. In fact, 41.5%(i) of blocked shots return possession to the team that was blocked. This can occur by either the blocked shot being returned into the hands of the offense or by parading out of bounds off the defense.
Swats out of bounds may get the crowd roaring, but softer, guided blocks can lead to better defense. When the ball is batted out of bounds or into the hands of the opponent, they get another opportunity to score, albeit with a shorter shot clock.
Attempts at blocks and even successful blocks can lead to easy offensive rebound clean-ups. Embiid goes for the block, but against the smaller Alvarado could stand to stay straight up and contest rather than jumping behind the basket leading to no contest on the Willy Hernangomez put-back.
Additionally, attempting blocks can lead to shooting fouls. What Poeltl does here isn’t necessarily wrong, just late. If Murray doesn’t fall asleep on the cut, Poeltl does not have to attempt the last second save leading to an and-one.
Blocks do not equate to good defense, but they also do not equate to bad defense. Blocks have their downsides and their perks; it requires a good team defense to harness their utility. If a team wants to get the most out of their blocking threats, they need to put players in position to make these plays infrequently and use their threat to block to deter players from taking shots close to the rim.
(1) Blocks per 100 possessions and defensive rating have a correlation coefficient of 0.082. Closer to 1 is direct correlation, closer to 0 is no correlation, and below 0 is an inverse correlation.
(2) Block percentage is the percentage of shots on the floor blocked by the individual player. The player is not necessarily guarding the opposing player who is taking each shot.
(3) Limited to those who contested at least 80 shots within six feet of the rim in the 2022 regular season.
(4) Since a shot near the rim has a 61.3% chance of going in, each shot is worth 1.23 points which would lead to no better than a 123 defensive rating if all shots were from this range; easily worst in the league.
(5) Golden State attempts to run a pin-down screen for Kuminga distracting Vanderbilt, but Vanderbilt doesn’t pay Kuminga any mind since he shoots 33.6% from behind the arc. If this was a better 3 point shooter, this may have worked.
(6) Williams also perfectly times his block attempt. He does not leave Capela, a lob-threat, until Huerter has committed to the lay-up.
all statistics taken and derived from basketball-reference.com and nba.com/stats unless otherwise noted
(i) https://squared2020.com/2017/12/20/making-blocks-count/
