Baseball Digest Daily interviews Bill James on the 2006 Fielding Bible Awards. Here he talks about Mike Lowell:

Mike Lowell is the best defensive third baseman in baseball. He's extremely interesting to watch. He keeps his glove hand, his left hand, very relaxed, and he doesn't appear to anticipate the hop at all. What I am saying is. .. the announcers, the veteran baseball people will tell you that the key to making the plays is to get your body in the proper position to make the play. But in fact, if you actually watch the fielders, very often they can't handle a tough hop or a line drive at an awkward angle precisely because they're trying to play the ball with their whole body. They're relying on positioning their body to make the play, and when something happens that makes that impossible, they're just SOL. Lowell, if you watch him, seems to be saying "it is easier to react with my left arm than it is to re-position my whole body in anticipation of the play." He stays balanced, stays loose, reacts late and has extraordinary confidence in his ability to snag the ball with his glove at the last moment. I've never really seen anything like it before, but this looseness and unusual confidence, for example, gives him a remarkable ability to charge a ground ball. He can change a slow grounder top speed because he knows that, bad hop or good hop, in-between stride or on stride, he can slap at the ball with his glove and pick it out of the air.

The interview is definitely worth the read.