Get tickets and join the crowds at a game at Balboa Stadium. If there's nothing scheduled while you're there, you might like to check if they give a guided tour of the facilities.
This Downtown San Diego sporting facility is a good spot to start your day of sightseeing. There's lots to do and see in the area, including San Diego Zoo, Balboa Park, and San Diego State University. Wander around at your leisure at Balboa Stadium before heading to these other fine sights.