Monday, February 19, 2007

Analysis: Has the offense or defense improved?

A question that has come up a lot recently on HoyaTalk is whether the team defense has improved over the course of the season.

We can use the Game Plan data to take a look (click on image to enlarge):

This plot shows the raw offensive and defensive efficiencies for each game played so far. From the plot, it looks like there has been an improvement in offense over the course of the season (multiply the slope by 30 days (~month) and you get ~5 ticks more efficient / month). Defensive efficiency, unfortunately, is also rising, albeit at a slower rate (~2.3 ticks / month), which would mean the defense is actually getting worse. Since G'town averages about 60 possessions / game, a "tick" ( = 1 point / 100 possessions) represents about 0.6 points, so Pomeroy suggests that the offense is improving about 3 pts. month, but the defense is giving back about 1.4 pts month.

However, these numbers don't take into account the quality of opponent. We can do that by multiplying G'town's Off. Eff. by the opponents Adj. Def. Eff., then dividing by the season average (101.7 on Feb. 19th), to produce a net offensive efficiency. This represents how well the Hoyas' offense performed, accounting for the average defensive effort of the opponent. The same can be done for G'town's defensive efficiency (note here that I've flipped the sign for Net Def. Eff., so that a positive number mean G'town played better defense than average against their opponent). Here we go:

Well, things look a bit different now. The offense, accounting for the better defensive teams played lately, is actually getting much better as the season goes on (~5.3 pts / month), while the defense is actually stagnant (0.1 pts / month). What else is obvious is that there are 3 games since Jan 1st where the defense has been lousy [@ Pitt - L (1/13), Cinci - W (1/27) and @ L'ville - W (2/7)], but for all other games since early December, the Hoyas have defended about as well as or better than average.

Now there's a lot more you can do with these stats. For instance, do Net Off. Eff. and Net Def. Eff. track? This could indicate either playing to the level of your opponent, or my pet theory, the influence of the refs on the game:

And there does seem to be a trend, although not as significant as expected. When the Hoyas play lousy on defense, they play better on offense, and vice versa. Hard to say if this is just the result of how tightly the game is called, or another factor. I'll need to look at this more closely down the road.

We can also break out offensive and defensive efficiencies into their constituents, and look for trends. Here, I'm using the same technique, comparing how well G'town performed in each of the four factors against the average performance of their opponent.

Offensive Efficiency Components

Defensive Efficiency Components

For these charts, the correlations on the left are eFG%, TO% on the top, OR%, FTR on the bottom. Now admittedly, these are a bit of a mess (as always, click on image to enlarge), but from the top chart, you can see that 3 of the four factors are improving; only free throw rate (the number of FTs per possession) has remained flat.

Defense is much more interesting. The most important factors, eFG% and turnovers created, have remained flat, but Georgetown seems to be giving up more offensive rebounds while fouling less. Not sure what to make of it; perhaps the team is playing more zone defense, which is reducing fouls at the expense of rebound position, but that is just conjecture.

Sunday, February 18, 2007

Analysis: Using KenPom.com's Game Plan page

When you look at the Game Plan page for Georgetown, below the table for individual game performance is a list of correlation coefficients for offensive and defensive efficiency versus various statistics, such as pace, effective field goal percentage, turnover percentage, etc.

Here's the correlation table, as of Feb 18, 2007:

                       Correlations
to OE to DE
Pace: -0.41 -0.20

eFG%: +0.72* -0.09
OR%: +0.35 -0.22
TO%: -0.60* -0.44
FTR: +0.13 -0.09

Opp eFG%: +0.20 +0.77*
Opp OR%: -0.26 +0.57*
Opp TO%: -0.17 -0.39
Opp FTR: -0.32 +0.29

Bold values are significant with a 95% confidence
Bold* values are significant with a 99% confidence

For Georgetown, Off. Eff. is well correlated with Eff. FG%, TO %, and pace, in that order. Def. Eff. is well correlated with Opp. Eff. FG%, Opp. Off. Reb. % and TO%, in that order.

Let's look at one of these correlations in more detail (click on image to enlarge).


















Here's a plot of Off. Eff. vs. Pace for Georgetown for the season so far. You'll note that the R^2 value in the plot is equal to the square of the correlation in Ken's table (-0.41 x -0.41 = 0.168). You'll also notice that there is a pace outlier for the dataset, namely the Vanderbilt game, with 73 possessions. For the season as a whole, Hoya games average 58.5 possessions, with a standard deviation of 4.6 [58.5 ± 4.6]. At ~95% CI (2 st. dev's.), the range is 49.4 - 67.7 possessions, so only the Vanderbilt game stands as an outlier.

If we remove it from the data set and re-run the numbers, the new plot looks like:


















Well, a couple of things jump out here. The correlation is much stronger (r = -0.547), and the slope of the line is much steeper (pace has a larger effect). If you remove the Vanderbilt game from the data set and re-run Pomeroy's entire table, you'll find that the OE vs. pace correlation is the only one that shows a significant change (i.e. other than pace, the game was typical for Georgetown):
                        Correlations
to OE to DE
Pace: -0.55 -0.27

eFG%: +0.72* -0.09
OR%: +0.36 -0.22
TO%: -0.61* -0.44
FTR: +0.13 -0.10

Opp eFG%: +0.20 +0.77*
Opp OR%: -0.26 +0.58*
Opp TO%: -0.17 -0.39
Opp FTR: -0.34 +0.30

Bold values are significant with a 95% confidence
Bold* values are significant with a 99% confidence


Well, this is all fine and good, but I'd like to take the analysis of pace effects a bit further, hopefully later this week.

Extra: Sapp's Long Three

Here's Jessie Sapp's 55 (60?) foot three-pointer to end the 1st half against Villanova on Sunday (higher res. version here).



This shot turned out to be the margin of victory.

Introduction

I thought I'd present some data analysis for feedback.

I don't claim to be any sort of authority on basketball or statistical analysis, just a Georgetown fan with too much time on his hands.

The basic premise here is that information can be gleaned about team performance from the pace-independent statistics, such as those generated by Ken Pomeroy. To start things off, I'll look at the individual game stats found on his Game Plan page, I'm hoping to identify trends and relationships beyond the basic correlations between certain variables and offensive or defensive efficiency.

Ken Pomeroy attempts to account for level of competition with his "adjusted" statistics, which are available for pace, offensive efficiency and defensive efficiency. The underlying statistics for efficiency calcs are only available as raw. My analysis looks at both sets, so I will try to note whether I'm using adjusted or raw statistics, or a mixture of both.

Saturday, February 17, 2007

Final score: Georgetown 58, Villanova 55

  Georgetown vs Villanova  
02/17/07 Noon at Wachovia Center (Philadelphia, Pa.)
Final score: Georgetown 58, Villanova 55

Georgetown Min +/- Pts 2PM-A 3PM-A FTM-A FGA A Stl TO Blk OR DR PF
Summers, DaJuan 34:51 + 8 11/53 2 -5 0 -4 7 -8 9 /43 2 /17 0 /52 2 /53 4 /31 3 /28 3 /34 2
Green, Jeff 39:34 + 5 19/58 7 -14 1 -2 2 -3 16/47 4 /13 1 /57 2 /58 8 /35 2 /30 7 /36 2
Hibbert, Roy 18:07 + 6 4 /28 2 -4 0 -0 0 -0 4 /23 0 /8 1 /24 1 /26 2 /18 1 /15 2 /20 4
Wallace, Jonathan 34:46 - 4 2 /49 1 -4 0 -1 0 -0 5 /42 5 /17 0 /49 2 /49 0 /32 0 /27 1 /31 1
Sapp, Jessie 40:00 + 3 16/58 3 -6 3 -4 1 -2 10/47 3 /15 0 /58 2 /59 0 /35 0 /30 5 /36 1
Macklin, Vernon 08:20 - 8 0 /7 0 -0 0 -0 0 -0 0 /8 0 /3 0 /12 1 /12 0 /6 0 /5 1 /6 1
Rivers, Jeremiah 05:14 + 7 0 /9 0 -0 0 -0 0 -0 0 /5 0 /3 0 /9 0 /10 0 /3 0 /3 1 /5 1
Ewing, Patrick 19:08 - 2 6 /28 1 -1 1 -2 1 -2 3 /20 1 /8 0 /29 1 /28 0 /15 1 /12 1 /12 1
TOTALS 40:00 58 16-34 5 -13 11-15 47 15/21 2 /58 13/59 14/35 8 /30 23/36 13
0.471 0.385 0.733 0.714 0.034 0.220 0.400 0.267 0.639

Villanova Min +/- Pts 2PM-A 3PM-A FTM-A FGA A Stl TO Blk OR DR PF
CLARK, Shane 35:38 + 0 6 /52 0 -4 2 -3 0 -0 7 /49 1 /16 0 /50 1 /51 0 /31 1 /32 2 /26 4
SUMPTER, Curtis 34:13 + 3 15/50 3 -6 1 -5 6 -6 11/46 1 /13 0 /50 4 /50 2 /31 2 /29 6 /29 4
SHERIDAN, Will 28:08 + 0 5 /42 2 -8 0 -0 1 -2 8 /34 2 /12 1 /39 0 /37 2 /24 3 /22 3 /17 1
REYNOLDS, Scottie 28:16 - 2 18/42 3 -8 4 -6 0 -0 14/45 4 /8 2 /45 1 /46 0 /25 1 /31 3 /21 4
NARDI, Mike 33:25 - 6 2 /44 1 -4 0 -2 0 -0 6 /44 2 /14 0 /48 2 /47 1 /29 0 /31 1 /25 0
REDDING, Reggie 16:23 - 1 6 /20 1 -1 0 -1 4 -6 2 /16 0 /4 2 /25 0 /24 0 /10 0 /13 2 /12 2
CUNNINGHAM, Dante 23:57 - 9 3 /25 1 -4 0 -0 1 -2 4 /26 1 /5 1 /38 1 /35 0 /20 3 /22 2 /20 3
TOTALS 40:00 55 11-35 7 -17 12-16 52 11/18 6 /59 10/58 5 /34 13/36 22/30 18
0.314 0.412 0.750 0.611 0.102 0.172 0.147 0.361 0.733

Efficiency: Georgetown 0.983, Villanova 0.948
eFG%: Georgetown 0.500, Villanova 0.413
Substitutions: Georgetown 34, Villanova 34

2-pt Shot Selection:
Dunks: Georgetown 5-5, Villanova 0-0
Layups/Tips: Georgetown 5-14, Villanova 5-13
Jumpers: Georgetown 6-15, Villanova 6-22