Introducing defensive score sheets

Phil Sears-USA TODAY Sports

Tomahawk Nation is the only place on the interwebs where you'll find actual analysis of Leonard Hamilton's defense

Modern basketball statistics were born over 50 years ago when Frank McGuire had his 26-year-old assistant coach Dean Smith begin tracking statistics based on possessions rather than raw numbers per game. The next major leap came in 2003 when Dean Oliver published his groundbreaking work Basketball on Paper which kick-started the movement toward advanced quantitative analysis. And on the college level, that's where we're at. We're still waiting for the next breakthrough.

What is missing is a smart way to evaluate individual defense. Steals and blocks are nearly meaningless if they aren't put into a deeper context, which leaves defensive rebounding as about the only stat with true value. But DR% is only a tiny sliver of what makes a good defensive player.

So to understand defense, you have to break down film. The first major effort to accomplish this came in 2011 when Sports Illustrated's Luke Winn teamed with David Hess (who now is a developer for Team Rankings) to evaluate several elite college defenses (including Florida State). They began with Dean Oliver's writing on defense, and developed Defensive Score Sheets (DSS). DSS are essentially a defensive box score, and the creation of that box score requires someone with a solid understanding of basketball X's and O's to watch film of every possession and assigning blame or praise based on what happens.

So I figured I would try it out.

The rules are simple. I can only chart games that are broadcast on television. ESPN3 doesn't work because some possessions require rewinding to watch as many as 8 or 9 times, and ESPN3 doesn't have an intelligent interface for that. So FSU's games vs Jacksonville and Tennessee Martin could not be charted. Also, the VCU broadcast was so screwed up that that game cannot be charted either. So for now, we have UCF, Michigan, Northeastern, and Florida.

Before I get to the results, here is a glossary taken from David Hess.

  • Taken from the box score
    • Min – Minutes played
    • DREB – Defensive REBounds
  • Tracked by me
    • FM - Forced field goal Miss – when a defender forces an offensive player to miss a shot from the field. Oliver separates FM from Blocks, but I’ve lumped them together here.
    • FTO – Forced TurnOver – when a defender forces an offensive player to turn the ball over. Again, Oliver separates out Steals, but I’ve combined them, partly because because I don’t know which plays the official scorekeeper would actually count as steals. One thing to note here is that a player who draws an offensive foul is always credited with a FTO, even if it’s just a moving screen.
    • FFTA – Forced missed Free Throw Attempt – missed foul shots resulting from a defender’s foul
    • DFGM – allowed Defensive Field Goal Made – when a defender allows an offensive player to score a field goal over him or by dribbling by him
    • DFTM – allowed Free Throw Made – made free throws resulting from a defender’s foul
  • Calculated Tallies
    • Stops – the credit a defensive player gets for actions that contributed to ending an opponent possession. This isn’t as simple as adding FM + FTO + 0.4*FFTA, because the credit for a missed shot has to be shared with the defensive player who rebounds it. The formula is more complex than you might think, and includes a sliding weight for FM vs. DREB, based on how difficult those actions seem to be in each particular game, so I’ll just refer you to Appendix 3 of Basketball On Paper.
    • ScPos – Scoring Possessions allowed by a player. This is essentially just DFGM plus a FT-related factor. I’ll again refer you to Basketball On Paper for details.
    • DPoss – [Stops + ScPos] – total Defensive Possessions that were credited to (or blamed on) a player.
  • Calculated Metrics
    • Stop% – [Stops/DPoss] – the fraction of an individual player’s credited defensive possessions that ended with 0 points. Essentially the inverse of offensive Floor%.
    • %DPoss – [(Min/40)*DPoss/TeamDefensivePossessions] (for a non-OT game) - the percentage of team defensive possessions faced by an individual defender. Analogous to %Poss on offense.
    • DRtg – [(1–%DPoss)*TeamDRtg + %DPoss*(100*TeamDefPtsPerScPoss*(1-Stop%))] – individual Defensive Rating. Gives a player credit for stops and scoring possessions he was directly involved in, then assumes a nebulous team-average performance in the other possessions. This is the analog of offensive rating.
I'll jump right in with the season long chart, as that has the most value. (click to enlarge)
Dss_total_medium

The most important place to start is on the far right, with DRtg. This corresponds with offensive ratings that we are all (hopefully - read you fools!) familiar with. Essentially, that is the number of points that player allows per 100 possessions. So low numbers are good (and shaded green). The %DPoss shows how often each player is involved in the play on defense.

Aaron Thomas has the best defensive rating on the team, to date. If you compare the %DPoss for Thomas with the next best defensive ratings  (Montay Brandon and Ian Miller) you'll see that not only does Thomas allow fewer points, but he is also involved in more plays. So it's key to think about those two stats in tandem.

On the other end of the spectrum, Michael Ojo has the worst DRtg on the team. This is primarily due to the obscene number of fouls he commits (9.3 per 40 minutes), which creates a parade to the foul line. The Ojo did have the best individual defensive rating for the Florida game though, so there's hope.

I'll post the individual games below, and am happy to help with any questions in the comments section. And this is a season long experiment, so I will follow up at regular intervals throughout the season.

Dss_ucf_medium

Dss_michigan_medium

Dss_northeastern_medium

Dss_florida_medium

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