[BoutPractice]

Kobe used to be a very good defender (though not as spectacular as his accolades suggest).
Now he's become a liability. And it's not because he's old or slow, strangely enough it's because he doesn't seem to try anymore and makes simple mental mistakes, often forgetting where his opponent is.

Incidentally, I would say off the ball defense is both more important and more unappreciated than on the ball defense.
Losing track of a player you're supposed to guard, not contesting the passing lane, gambling and allowing him to make a backdoor cut, rotating to the wrong player, not rotating at all, not hedging on pick'n'rolls for big men... Those kill teams.