You can evaluate the defensive contribution of a single player by looking at the team ratings, tactics, and the individual ratings. The player rating heavily depends on their defensive abilities/contribution. So, a guy who goes 1-10 and gets zero rebounds may have as high a rating as a guy who goes 7-10 and gets 3 rebounds with same minutes. This suggest he played better defence.
It's obviously not very simple, but you should get a good feel after a couple of games.
Well, enthusiasm level influence those ratings (it is the same for the whole team so no problem) but I believe game shape influences it too, so I wouldn't say looking at the rating in comparison to stats (and minutes) is a good way to guess defensive skills of a player. Looking at how his man was succesful in the game is a better way (matchup ratings included).