(The Pacers are Good at Defense, Run on the Heat, the Lakers are Weird and Other Lessons from Prior Event Data)
If you listen to Doc Rivers, and many other NBA coaches, they will tell you that the key to the offense is their defense and getting stops. There are a couple of reasons for this, I think, all of which are good. Part of it may be just motivational, for basketball players at every level it is sometimes harder to motivate effort on the defensive end as many popular gifs of James Harden will testify. Defensive effort is also something players and coaches can control unlike whether shots fall, though they can maximize the expected efficiency of those shots, bounded by what the defense gives them. Lastly, it's probably true.
Using the data from NBAWowy.com, I aggregated the effective field goal percentage for each team defense after different 'Prior events' taken by NBAwowy from the Play by Play data. The events tracked are made baskets, defensive rebounds, offensive rebounds, steals, other turnovers, time outs, and non-shooting fouls. The data only tracks the last event before an attempts basket, so it doesn't tell us about free throw attempts or possessions that end up in turnovers before an attempts is made. But, even without that layer of detail, I think the Prior Event data tells us some interesting things about game flow and defense. In fact, the possessions that lead to the highest eFG% such as following steals probably lead to the highest number of free throw attempts given that those possessions lead to attempts at the rim most often.
Below are the Prior events to a field goal attempt with the eFG% of every team's opponents with data through 11/28 (note that the league average for offense should be the same):
|FGM/FTMeFG%||DRB eFG%||ORB eFG%||STL eFG%||TOV eFG%||FOUL eFG%||TIME eFG%|
Those numbers are all very similar to ones compiled by Evan Zamir, the creator of NBAWowy, last year. This year's numbers already represent over 37,000 field goal attempts, so I think we are getting some real signal in the data. Of note is that steals or live ball turnovers are the by far the most efficient start to an offense and the toughest position for the defense, while attempts immediately after time outs were the least advantageous for the offense and the best for the defense.
Coming off a time out the offense's eFG% is 4.9% lower than following a defensive rebound. Yet noticeably too many coaches call time outs after a defensive rebound in late game situations, which probably speaks of both unfamiliarity with the stats, and a desire to attain the illusion of control over the situation. But, the coach should trust his offense and let the players play it out.
Looking at the data for the league and on a team level, it struck me that a useful way to group the Prior Events is as 'Dead Ball' events, or, Out of Bounds Events; made baskets, turn overs, fouls and time outs, and 'Live Ball' events; defensive rebounds, offensive rebounds, and steals. I grouped the opponents' eFG% weighted by the number of possessions after each Prior Event and calculated the average for each team and then league wide. The league wide averages showed about a five percent gap between shots after stopped ball events and live ball events favoring the defense.
|Stopped Ball||Live Ball|
In terms of individual team defense there are a couple of interesting bits to pull out of the split between Stopped Ball and Live Ball events:
- The best team off of any Stopped Ball event, and second best on Live ball events so far is the stifling defense of the Indiana Pacers with opponents shooting at eFG% of 39.2% after any out of bounds situation and 45.6% after Live Ball prior events.
- Most teams, 26, are allowing opponents to shoot a higher eFG% after Live Ball events, with three teams allowing a marginally higher eFG% after Stopped Ball events.
- The Lakers are weird. They are allowing the highest eFG% after out of bounds events and the lowest after Live Ball events. That is driven by a league high 54.5% Opponent's eFG% after made baskets and a league lowest 39.7% after defensive rebounds. That seems like random noise to me, since I have no coherent explanation.
- The Heat have the largest gap between stopping opponents after Live Ball events and out of bounds events, allowing 45.1% eFG after a Stopped Ball event and a porous 58.2% coming off a Live Ball event.
- The Pistons have been the worst team defense coming off of a live ball event, particularly off of defensive rebounds, allowing opponents to hit at 59.7% eFG.
- There is only a small variation in the number of Live Ball to Stopped Ball events between teams. But the Bucks have been putting their defense in the toughest positions with a near even split in Stopped Ball and Live Ball events. While the Raptors, to my surprise, have put their defense in the best position with 56.8% percent of their opponents shots coming after an out of bounds situation where the defense has had time to set.