Buy a ticket to see a game at Stadium Merdeka. If there's nothing happening while you're there, you might like to check if they give a tour of the grounds.
This sporting facility is on the to-do lists of many visitors to Kupang. But Stadium Merdeka isn't the only drawcard in the area. Kupang Harbor, Pura Oebananta, and East Nusa Tenggara Museum are some other worthwhile sights nearby.