Grab tickets to watch a game at Tokyo Metropolitan Gymnasium. If there's nothing scheduled while you're there, you might like to check if they give a guided tour of the grounds.
Tokyo Metropolitan Gymnasium has an entry fee, so grab some cash and travel to the commercial neighborhood of Sendagaya. Wondering where to next after the sporting facility? Tokyo Sky Tree, Tokyo Tower and Tokyo Imperial Palace are some nearby sights worth a visit if time is on your side.