Why do we love rivalries? Why do we love to suffer with our favorite teams? Sam Sommers is a professor from Tufts University and co author of "This Is Your Brain On Sports." He tells us why we're wired the way we are!

“Rivalry is an amazing thing, and we know about it from a fan standpoint by anyone who’s been to a Yankees Red Sox game, or talking other parts of the country like Duke and North Carolina basketball or Ohio State and Michigan football. Rivalry does amazing things for the players, the performers themselves. They do these studies in rugby or soccer and they measure the physiology or work rate of the players on the field. You run harder, you work harder. You actually have surges of testosterone when you’re playing against your heated arch rival as opposed to just your average game against someone else in another division. Something about knowing you’re pitted against your rival makes you perform better. It’s the same thing when you’re in a 5K at a running club, or when you’re on eBay and you’re bidding against StarKitten369 whatever, you know who that person is, you work up and energy, you get more aggressive, you bid more actively. Have an identifiable arch rival elevates our performance. It changes the fan’s mentality, but it changes it for players, too.”