When an athlete is honored with the title of captain, several things are instantly expected of him.
A captain's job, first and foremost, is to set a high standard of professionalism for his teammates to emulate. Several players on this list failed to do this—either by breaking league rules, losing their temper on the field or the like—and these players have been ranked higher than their counterparts who only struggled statistically.
A captain should also perform at a high level on the field. One of the best ways to judge on-field performance is by referring to statistics (although this is debatable), so you'll see a couple guys on this list who simply didn't put up the big numbers expected of an athlete in a position of leadership.
A captain should also help led his team to victories, therefore you'll notice that no player on this list was a member of a playoff squad in 2011.
I could have inadvertently left some players off this list. So if you have an opinion of your own, let me hear it!