Rampant speculation from Jonah Lehrer on why people care so much when they watch overpaid athletes play sports. It is, perhaps, all about mirror neurons:
"The main functional characteristic of mirror neurons is that they become active both when the monkey makes a particular action (for example, when grasping an object or holding it) and when it observes another individual making a similar action." In other words, these peculiar cells mirror, on our inside, the outside world; they enable us to internalize the actions of another. They collapse the distinction between seeing and doing.
This suggests that when I watch Kobe glide to the basket for a dunk, a few deluded cells in my premotor cortex are convinced that I, myself, am touching the rim. And when he hits a three pointer, my mirror neurons light up as I've just made the crucial shot. They are what bind me to the game, breaking down that 4th wall separating fan from player. I'm not upset because my team lost: I'm upset because it literally feels like I lost, as if I had been on the court.