If you're watching a college basketball game in person, chances are you're in an arena — a building specially designed for sporting events and large-scale rock concerts.
There's not much difference between an arena and a stadium, although an arena is enclosed and a stadium sometimes has an open roof. Football is usually played in a stadium, while basketball and other sports typically hold their games in arenas. The word arena originally meant "place of combat," and it's sometimes still used this way. Its root is harena, a kind of sand that was supposedly used on the floor during ancient Roman battles to soak up spilled blood.