RealGM

Based purely from a statistical look.

99 DRTG
2.5 STL%
6.5 BLK%
+0.4 Def On/Off
108.1 Team DRTG (24th of 30)

How do you reconcile the high individual DRTG with the poor on/off and team DRTG? Obviously Drummond was limited by minutes and injury, but that's still a huge gap.

10 games started and 20.7 mpg on the season; how much impact could he have ever had?

For a young rookie, that his defensive on/off isn't a disaster is a very good sign of things to come.

And in limited minutes, he's not going to turn a Detroit team with many other problems into a strong defense.

He played alot of his minutes with Bynum, Villanueva and Daye.

Well, he's backing up Monroe, so his on/off stats will only be poor if he's a horrible defender. And Drtg is a bad stat. It just throws in box score stats like blocks/steals/rebounds to the team's defensive rating. That tells you very little. You know about a guy's blocks and rebounds already; that's easy to find.

His RAPM was -0.9 on defense, which actually isn't bad because RAPM models usually assume rookies are negatives generally. I don't know what the prior for rookies was this season, but I think -0.9 is better than the prior.

There is no one like him given his age and basic defensive stats:
http://bkref.com/tiny/FpPNY

If you relax the standards you get a weird list:
http://bkref.com/tiny/pWVXa

Yes, Anthony Davis, Shaq, and Biedrins.

For lineup analysis, comparing lineups with a guy replacing Drummond, here are some sets:
Knight-Stuckey-Singler-Monroe-Drummond, 116.4 minutes, 1.14 def rating
Knight-Stuckey-Singler-Maxiell-Monroe, 63.1 minutes, 1.03 def rating

Knight-Stuckey-Prince-Monroe-Drummond, 68.7 minutes. 0.97 def rating
Knight-Stuckey-Prince-Maxiell-Monroe, 265 minutes, 1.04 def rating

Calderon-Knight-Singler-Monroe-Drummond, 56.1, 1.15 def rating
Calderon-Knight-Singler-Maxiell-Monroe, 226.3 minutes, 1.05 def rating

So according to that Maxiell is a much better defender? That seems like a stretch. RAPM had Maxiell at +2.4 though.

Given that he was a young freshman in college who went to the NBA after one year, what you really want is defensive potential, and he grades out well here. Drummond has a 9' 1.5" standing reach and a 7' 6" wingspan, which are good numbers for a center. I always saw Drummond as a young Howard, and Howard has a couple inches in standing reach but a couple less in wingspan, oddly enough. If Drummond gets a good defensive coach and puts in the work, I could see him like the next Dwight Howard though probably a little weaker. Howard had a sprint time of 3.14 seconds, by the way, which is something you'd expect from a guard, but Drummond was only at 3.39 seconds. So I think his overall defense will have less of an impact than peak Howard, but in the paint and on the glass he should be able to approximate him.