If your teen has a group of friends around, set them up with an outdoor activity that won’t seem too childish, such as a camera scavenger hunt. Most teens have cameras on their cell phones, so give them a list of objects they have to hunt for in your yard, neighborhood or town. They’ll scavenge through the area to find the objects and take a photo; options include a colorful leaf, a person on a swing or an object that is their favorite color. The first team to bring back all their pictures wins.
For a more sport like event, set up a game of Capture the Flag. Divide the teens into teams of two, split your property into “territories” and give them each a flag that they must place visibly yet inconspicuously in their territory. Each team's goal is to cleverly snag the other team’s flag without being caught.