Kevin Martin is a bit skinny. Actually really skinny. He should weigh much more than 190 because of his height. But I think he will gain more weight over the next few years in the NBA.
How much was Doug Chistie in his 3rd year? That's a more accurate comparison. Also, Kerry Kittles was a good defender. I think Rip Hamilton is a pretty good defender too. Actually, I've always compared Martin to a hybrid of Kerry Kittle/Rip Hamilton. Really, I think he's more than capable of holding his own on defense.
I think at the moment that Kevin is a decent defender on the perimiter, with the quickness to get better,if he has the desire, and I think he does. However, he will have problems with post up 2's until he puts on a little more muscle. I wish him luck trying to guard, oh, lets say Bonzi for example.
It's not cast in stone that Kevin will automatically guard the other 2 on the floor. For example, with a post up 2 like Bonzi, we might easily see Ron shift. In fact, I might even look forward to seeing that. It could be interesting.
Has there ever been a good defensive 2 guard who is 190 lbs?
I can't think of anyone. There have been plenty of good PG's at that weight (Payton, Kidd), but not 2 guards.
The reason I pose that question is because it is impossible for someone to be a good defender at that weight guarding the best players in the League (LeBron, Kobe, Wade, TMac, Manu) and giving up 25+ pounds.