Grab tickets to see a game at Stade Olympique. If there's nothing scheduled while you're there, you might like to check if they give a tour of the facilities.
You'll find this attraction in Nouakchott. Pay the entrance fee and then explore at your own speed. Once you're done at Stade Olympique, head for nearby sights like Nouakchott Beach, Mosquée Marocaine and Marche Capitale.