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A study of the value of blocked shots

"A crisp pass leads to an open path to the hoop. The receiving player palms the ball in one hand as he elevates to the rim for the show-stopping dunk -- but wait! From the weak side comes a towering foe, arms extended, and feet also leaving the ground, intent on mid-air contact of a different sort..."

The scenario plays out many times a game, and can represent some of the more exciting moments in basketball as two players collide with contrary objectives. Nevertheless, for all the drama, we have unanswered questions regarding the true significance of a blocked shot. How often for instance does the blocking team get the defensive rebound? Does a block frequently lead to ensuing high percentage transition shots? And arguably most important, what's the effect on the team whose shot was rejected on ensuing possessions?

In trying to address these points, we'll query our database for some facts on what's happening in the shot-swatting arena in the NBA 2003-04 season so far.

1) General Blocked Shot Percentages
If you exclude tip shots, which are very rarely blocked, the overall percentage of shots that have been re-directed in the NBA this season is 6.6%, or in other words about one out of every fifteen shots.
Shot Type
Blocked %
Jumper
3.8%
Close Up
14.2%
Dunks
2.7%
Totals
6.6%
What it amounts to then is the close-in action. Jump shots get knocked aside once in a while, particularly a shot taken in traffic, and it's even harder hard to block a dunk, but one in every seven shots from close to the hoop gets rejected.
The "Close Shot" findings are significant in light of the fact that the league average field goal percentage on such attempts stands at 53.3% -- if the defense doesn't block the shot there's a 62% chance it's going in! Perhaps next season we'll begin charting "shots altered" because clearly in a number of cases there may be no block but still a formidable defensive impact.

2) Blocked Shots by Shot Clock timing
Another consideration is that perhaps the time left on the shot clock has some influence over the likelihood of a block. It would seem logical when the clock is winding down and the defense knows a shot has to be launched quickly there would be a better chance at casting it aside.
Shot Type
0-10
11-15
16-20
21+
Jumper
3.7%
3.7%
4.0%
4.1%
Close Up
13.5%
14.7%
14.9%
15.5%
Dunks
1.7%
3.8%
4.5%
7.0%
Totals
7.0%
6.3%
6.4%
6.2%
As it turns out, each individual shot type shows the right flow of being blocked more often later in the shot clock. However because the distribution of shot types is not consistent across the seconds, the total numbers don't concur.
What we are seeing here is that in the quick shot category you have a lot more close up shots, and thus in spite of a lower "close block %" the overall average gets spiked. An argument could be made that breaking out the 0-10 second category by fast break shots, shots off an offensive rebound, and shots off an inbounds play would be helpful.

3) Blocked Shots by Position of the Shooter
Some of the uglier (or standout, depending on your perspective) blocks occur when a little guy tumbles into the lane and throws up a shot amidst the "tall trees" -- but is there any truth to the notion that the shorter players get their shots blocked more frequently?
Position
All
Jump
Close
Dunk
PG
5.3%
2.9%
13.3%
2.9%
SG
5.0%
3.1%
12.8%
2.1%
SF
6.2%
3.6%
14.1%
1.7%
PF
7.6%
4.5%
15.1%
3.3%
C
9.6%
6.9%
15.4%
2.9%
The answer is a resounding no! It's actually the big guys who get their shots sent back the most. "The better part of valour is discretion," Shakespeare wrote, and the short guys in the league seem to take this to heart. Of course they're not getting double-teamed or trading elbows.
Indeed the fact the centers have their shots blocked nearly twice as often as point guards on a league wide basis reflects the reality that on virtually every shot they take they are going against the other team's top shot blocking force.

4) Blocks by Position of Shot Blocker
This next category seems predictable -- the majority of blocks must come from the centers and power forwards right?
Blocker
All
Jump
Close
Dunk
PG
5%
8%
4%
3%
SG
9%
12%
7%
9%
SF
13%
14%
12%
7%
PF
28%
26%
30%
31%
C
45%
40%
48%
51%
The numbers represent the percentage of total blocks that come from the player at that position in the five-man unit.

As expected, the power forward and center positions account for almost 3/4 of all blocked shots in the NBA.

5) Defensive Rebounding Percentage after a Block
All right, enough of the easy stuff, let's tackle a more serious question: how often does the shot blocking team recover the ball after the swat?
Shot Type
Def. Rebound %
Jumper
58%
Close Up
56%
Dunks
73%
Totals
57%
An NBA shot in general has about a 71% chance of being claimed by the defense, so clearly the block allows for a better offensive rebounding opportunity. In part this is because on almost one in six blocks the ball goes out of bounds and is returned to the shooting team.
The 57% overall mark though is still some ways from an even 50/50 pure loose ball, and so better than half of blocks are not only a noticeable event, but lead to a defensive stop. One might think that different players would have different "recover rates" particularly if they were less inclined to knock the ball into the seats and more inclined to keep it in play.

6) Def. Rebounding Percentage after a Block by Position
Does the position of the shot blocker make a difference as to the expected chance of the defense getting the rebound?
Blocker
All
Jump
Close
O/B*
PG
50%
56%
41%
23%
SG
56%
58%
52%
22%
SF
54%
55%
53%
20%
PF
56%
58%
55%
16%
C
58%
59%
58%
14%
We omitted blocked dunk shots since the sample gets so small, and inserted a column with the percentage of blocks that go out of bounds and are awarded to the offense. Defensive rebound rates do not vary by a significant difference for blocks by big men, but the "out of bounds" problem is lessened.
We could also produce the chart for "defensive rebounding rates after a block by shooter position" but there's very little to be learned from that -- the 'All' numbers work out to be PG 56%, SG 59%, SF 55%, PF 57%, C 57%.

7) Leading Shot Blockers by Def. Rebound % After Block
As we wrap up part one of this exercise (cagey readers will have realized we've saved the meatier issues for the second half), we'll finish on a light-hearted, player specific note: which players with at least 30 blocks on the season have seen their teams secure defensive rebounds on a high percentage of the rejected shots?
Player
Team
Def. Reb%
O/B*
 Ostertag
UTA
69%
10%
 Bosh
TOR
69%
9%
 James
SEA
69%
3%
 Thomas
WAS
67%
12%
 Smith
MIL
66%
16%
 O'Neal
IND
64%
8%
 Ratliff
ATL
63%
8%
 Garnett
MIN
63%
14%
 Mutombo
NYK
63%
14%
 Dalembert
PHI
63%
14%
Ah, the unheralded Greg Ostertag winds up atop the list. He's something of a sentimental favorite for us since we have never received more abuse than what was heaped on us for having Ostertag ranked as the #7 player in the league last season on the Roland Ratings. Maybe he does do the little things well that don't show up in the box score.

Chris Bosh and Jerome James are running neck and neck with the current leader, and James' 3% O/B stat is spectacular.

Theo Ratliff got the initial nod from us in the leading shot blockers article, and it's good to see that not only does he block a healthy number of shots, but they get recovered at a higher than average rate and few go directly out of bounds (and back to the offense). You might also want to keep an eye on Philly's Samuel Dalembert, trust us, he's a keeper!

That's part one -- in part two we'll cover the average points per possession following the block for both teams, the effect on shot selection, and even a look at how the individual shooter performs on subsequent times down the floor.


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