Purchase tickets and join the crowds at a game at Kukulcan Stadium. If there's nothing happening while you're in the area, you might like to check if there's a tour of the grounds.
You'll be spoiled for sightseeing choice when spending time in Mérida. Kukulcan Stadium is an ideal place to kick off here, but there are many other fine spots to appreciate. Paseo de Montejo, Plaza Altabrisa, and Mérida Cathedral are close to the sporting facility and will fill in your day nicely.