Saturday, January 12, 2019

Calculating defensive rating for guarding opponents


In 2011, this post broke down the defensive calculations for the Value Add Basketball rankings for all college players from 2002 to the present. While the rankings received national praise, this continues to be the most underappreciated aspect of the rankings. While other systems rank a players defensive steals, blocked shots and defensive rebounds, they ignore the fact that these three together are less important than guarding your opponent and a player who scores a lot of points but allows opposing players to cut to the rim in 100-90 losses is not nearly as valuable as a player who scores even half as many points and helps his team pull out 50-40 wins.

Picking up on a recent CBS 247 site breakdown of Markus Howard's Big East record 53-point game against Creighton, below provides how the defensive rating is affected by the following calculations.

As good as Marquette’s defense has been this year, they were no match for Creighton’s
offensive scheme except for the absolute domination underneath led by Theo John’s blocks.
As good as the block he made while walling up was, his rejection off of the backboard so that it shot
back over four Creighton players in position was one of the best defensive plays I’ve ever seen.
We credit a blocked shot for taking 0.67 points away because 0.33 is reserved for the one-third
chance the offense gets the rebound. That block by John’s was worth the full 1.0 and even more
because he purposely blocked it so hard Creighton no longer has a chance for a rebound and in
fact he started the break the other way using the block like Wes Unseld use to use the outlet pass.


Running total
Figure
Explanation
4.85
4.85
More defensive rebounds than one-third of missed shot, worth one point each
(MU grabbed 29 of 35 CU misses, 4.85 more than typical 69%)
1.66
2.48
more blocks than typical based on number of 2-point shots taken worth
0.67 points each (CU 32 two-point shots typically result in 3.52 blocks,
but MU blocked 6)
-3.68
-3.68
more steals than expected based on trips down the court worth one point
each (MU 80 defensive possessions typical 5.68 steals, but only had 2 steals)

2.83

Total Points taken away (or added if a negative) based on blocks, steals and
rebounds
104.00

actual points scored by opponent
106.83

anticipated points allowed if if blocks, steals and defensive rebounds average
(total of the previous 2 numbers to reverse engineer)
82.16
80
how many points would have been scored if 1.027 per possessions in the game
-24.67

how good was the guarding defense based on points less than expected
not counting
blocks, steals and rebounds
-0.11
225
how good or bad (if negative) the guarding defense was after using the
number of minutes played in the game (200 if ends in regulation, add 25
for each overtime)
-4.72
43
based on the players minutes played, how many points did the player take
away or add with good or bad defense
A couple of other follow-ups to this post on the Marquette CBS 247 page is the following list of the
only possible plays in a game that Markus Howard did NOT have during the game and how
valuable each of those plays is.

Only things Markus Howard did NOT do in game
Value
Made 2-point show and drew foul (unassisted)
1.67
Made 2-point show and drew foul (assisted)
1.33
Steal
1
Draw 3-shot foul
1
Offensive Rebound
0.67
Draw 1-and-1 foul shots
0.11
Foul drawn but no free throws
0.1

Missed deadball FT, no rebound chance
-0.67
Miss front end of 1-and-1
-0.74

It appears the one thing a player can do that hurts their team the most in all of basketball is missing the front end of a 1-and-1, since an average free throw shooter scores 1.11 points per one-on-one opportunity, so in the just under 3 out of 9 times the front end is missed it means the player secured 0.00 or the average 1.11 points. However, because the team does have a one-third chance of an offensive rebound, there is a chance the get the miss and score so it counts as a -0.74. We do not have a way to break down the slightly lower chance of an offensive rebound on a free throw miss verses and attempted field goal.


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