Ok, so first off, the Mavericks defense isn't THAT bad. But it is pretty bad, 19th in the league in points allowed per possession for the season, but 16th over the last 20 days. The defense is getting marginally better, and the Mavs' offense has improved to the extent that they're actually running a positive net efficiency of about 2.7 points per 100 possessions over that 20 day stretch. Given how fond as we sports fans can be of hyperbole, I'm going to try not to overexaggerate our defensive situation here: it's supremely mediocre. But given that the Mavs have plenty of players with serious defensive promise (or who were once defensive studs, here's looking at you Elton) like Crowder, Wright, James, and Roddy B all being paired with Shawn Marion and the defensive mastermind that is Rick Carlisle, it's hard to imagine why they're so...not good.
But they are not good. And first things first: the defense really misses Dahntay Jones. He only got 6 minutes a game, but other than Roddy B he was the only player who could keep the team below 100 points allowed per 100 possessions (and a wonderful 94.3 at that) while on the floor.
So, that means that now Roddy B is the only really "efficient" defensive player on the roster. Which is telling. Because he's a point guard. And that's where the problems start.
I'll start with this shocking stat: the "usual" starting lineup of Darren Collison, OJ, Marion, Dirk, and Elton is really bad. They give up an absolutely horrendous 119 points per 100 possessions and score a paltry 97. But...Marion and Elton...right? Well, they're not really the problem. Everything starts with the high pick and roll and then just falls apart.
Here's what happens using the Rockets as my example because they did this PROLIFICALLY. So:
Montejunas -- the stretch four -- comes up and picks for Jeremy Lin -- the point -- at the top of the three point line.
Collison tries to tighten up on Jeremy Lin to hedge the pick, only to have Lin race past him because Lin is fast and Collison suffers from chronic Monta Ellis syndrome.
One of two things will happen with DC, either he'll do his best to catch up and crash the paint because he's athletic and fast and it works, or he'll scramble to recover his lost rotation and end up in a mid range void on the weak side blankly staring at the paint.
So now, Lin has handed the ball off to Montejunas, who's managing an Elton Brand-Dirk double team, because Montejunas got open on the roll and Elton moved in from the corner to contain the paint and Dirk is overcompensating.
Now, a wide open Omer Asik runs a wide open baseline cut, which makes Marion move too far off of Parsons -- the shooting wing.
This happened all the time against the Pistons tonight too: anyone notice how Jason Jerebko, an essential nobody, picked apart our defense? It was those open baseline cuts. How about those late game Charlie Vilanueva 3s from the corner? They were the result of overcompensation into the paint from the perimeter due to a collapsed outside pick and roll.
Now, even if the pick and roll collapses because DC pulls a Monta Ellis, there are ways to defend it. Watch the Bucks sometime and see how Larry Sanders totally EATS the rolling man while Mbah a Moute switches off to the cutter and Brandon Jennings compensates on the weak side perimeter. That's how the Mavericks need to play it: Collison needs to follow the ball handler in every scenario, ESPECIALLY those in which the handler heads to the perimeter, and when the corner big man cuts, we need the wing defender to rotate and THEN have the other perimeter defenders rotate with him.
Because this is the problem we have with Mike James. He DOES follow the ball handler post-pick, and he even rotates to the cutter sometimes (why we see so many Mike James post mismatches) but then the other perimeter defenders don't follow and rotate, and the result is a wide open three. While both Mayo and Vince Carter are solid defenders, both are prone to ball watching and don't tend to react to well to situations unfolding off the ball and the result is either open cuts or open corner threes.
There are two "perfect world" solutions for this problem: the Mavs either pick up a Larry Sanders type, who is terrifying enough to make a pick and roll stop at the free throw line and apologize, or a Tony Allen type who can contain the pick and roll ball handler. As it stands, Dallas doesn't have (and isn't super likely to get) either. What they can do is communicate better; learn to rotate in the right places, expect the ways in which the pick and roll has collapsed the defense and stop over-helping. They've already done a little better with this over the last few games, and hopefully, they'll only get even better over the rest of the season.