jermaine has definitely picked up his game on the defensive end today.
His slow/kinda lazy rotations are defense are a little annoying. ive seen him lose his man, or forget to switch back numerous times now. dont know if anyone else has noticed. maybe that stuff will go away once he gets more worked into the lineup.
Jermaine needs the second big man on the court to be very active off the ball in helping out on his man + on the backboards while he goes up for blocks.
Without that help, his defense gets exposed just as often as it helps ... which is pretty much what happened in Toronto with Bosh and Bargnani. For every shot altered or blocked shot Jermaine got, he gave up a layup off a pass or an offensive rebound and put-back.
In Miami, Udonis Haslem gave him that coverage and it worked well.
Here in Boston, Garnett will definitely be able to supply it. As could Kendrick Perkins. I think BBD should be able to do a solid job too.
Shaq? Not so much, at least not regularly. He doesn't move quickly enough to cover that ground. He'd need to be matched up against someone who plays very close to the rim and/or isn't much of an offensive threat.