If your goal is simply to see as clearly as possible, it may be preferable to wear contacts (rather than glasses) during sports. Unless your glasses were designed with sports in mind, they may fog up or slip down your face as you play. And in the event of a fall or errant ball, they may even shatter. That said, if your goal is to get added eye protection, to shield your eyes from the sun, or to reduce glare, glasses may be a better pick than contacts. Just make sure to buy a pair of sports glasses (not regular glasses), and make sure those sports glasses have the features you need them to.