See the Alamadome. 65,000 seats, designed for football and basketball. For basketball, spectator capacity was expandable to almost 40,000 seats for the playoffs (many upper seats were curtained off during regular season games). Of course, having seen basketball there myself, it was an awful place to watch a basketball game. The Spurs have since moved, so it doesn't matter. They got a new arena with capacity of about 18,000 or 19,000 now (I'm too lazy to look it up). I haven't been to the AT&T Center, but I hear it's decent. And more appropriately basketball sized. And of course, few seats makes it easier for the team to charge more per ticket and leave the real fans at home where they can barely pay their cable bill.
Don't ask what sort of Chunks they are, you probably don't want to know. Blowing Chunks since Season 4!