To someone who knows Underwoods system better than I, is the defensive problem based on poor rotations? I thought I had heard Lou Henson brag about Underwoods defense at OSU. Something is broken there.
Poor rotations is part of it, and lack of discipline and awareness to avoid fouling another, but lack of inherent rim protection and rebounding ability is probably the biggest part.
West Virginia gets blocks and one-and-done rebounds of misses forced by contests coming suddenly and from weird directions.
Illinois fouls and allows layups and second chance opportunities.
And for the record, Underwood's defense wasn't very good at OSU even when they made the system tweaks. And the defense was just okay and behind the offense in his first two years at SFA as well.
In a way the defense isn't meant to be efficient per se, it's meant as a vehicle for the way Underwood wants to play as a whole, generating fast break opportunities and not giving the opponent the opportunity to run offense and feel their way into the game. The offense and defense are part of the same whole, intended to be hard and frustrating to play against.
That has only very intermittently been the case at Illinois. Our opponents get rattled by the ball pressure at times, but you can see they've been coached to be patient and that there's a pot of gold at the end of the rainbow if they keep moving the ball and stretching the defense, which is true because we can't protect the rim.