This is going to be epic, so pull up a comfy chair.
Anybody who knows anything about basketball metrics knows that there are two major areas of improvement sought: 1) defense; and 2) “the little things”. Unfortunately, play-by-play data doesn’t really tell us much about “the little things”, but it can tell us something about defense. Currently, ezPM distributes credit or blame equally among teammates when the defense denies a bucket or allows one, respectively. The formula looks like this:
All the terms with “0.2” represent distributed credit/blame (for opponent 2pt FG, 3pt FG, missed FG, and non-steal turnovers). Because credit/blame is distributed equally, some players won’t get the credit they deserve, and other players will get more credit than they deserve for defense.
To begin to address this, I modified “the code” to keep track of the counterpart data for shots and assists. Once the data are collected, we can then modify the formula for defense. Here’s one way to do it (perhaps, the most obvious way):
Here, I’ve made no distinction between assisted and unassisted field goals. The “CP” refers to “counterpart”. Note that now every term, except for “TEAM_TAKE” (50% weight to non-steal opponent turnovers), is attributed to an individual counterpart. In theory, this should enable more accurate player valuation.
An alternative to the above formula that is worth considering is to distinguish between assisted and unassisted field goals, just as we do for offense:
Here, just as for the offense, I’ve split blame between the defender who “gives up” the assist and the one who allows the made field goal.
Now, it’s time to look at some of the results. Here are the top defenders as defined by (greater than 1500 possessions):
Note that the average position for the top 25 above is 2.56 (between SG and SF). Here are the 10 players who improve the most with over the original defense formula:
I was not expecting Steve Nash to be helped by counterpart defense. I suspect my readers share my surprise. Moving on, here are the 10 players hurt the most by :
Noah? That was not expected.
Let’s look at what happens when we take into account assists. Here are the top 25 defenders according to :
The average position here is 3.7 (between SF and PF). Maybe I’m crazy, but this actually makes more sense to me than the first metric, as big guys do tend to have more impact on defense — at least, that’s the conventional wisdom, right?
Here are the 10 players who improve the most:
And here are the players who lose the most with :
All point guards on this list. Now, the interesting thing is that I’m not sure that’s bad. Why? Because ezPM appeared to have a preference for point guards before. Why? For the same reason that point guards appear on this list. They get a lot of credit for assists, but don’t get debited for “missing” assists (or potential assists, which aren’t recorded). It’s sort of a win-win situation for point guards. So, in a way, you can think of this as a defensive correction.
Anyway, there are some really interesting questions that can and should be raised. I’ll leave you with this particular question. We know, or at least, the conventional wisdom is that assisted field goals are “easier” to make. That’s why I give an assisted field goal 70% of the credit that an unassisted field goal would receive. This raises an important question: On the defensive side, should we give more or less credit for giving up an assisted or unassisted field goal? If the assisted field goal on offense was easier to make, it would seem to follow that the defender should be debited a little less, right? That would justify debiting the player guarding the passer as well as the one defending the shooter. On the other hand, one could make the argument that the defender enabled the counterpart to get open and in a position where he could be assisted. See where I’m going with this? These are not simple questions in my mind. But we’re getting somewhere now, I think. To be continued…obviously.