Sportswear is typically designed to be light weight so as not to encumber the wearer. The best athletic wear for some forms of exercise, for example cycling, should not create drag or be too bulky.
On the other hand, sportswear should be loose enough so as not to restrict movement. Some sports have specific style requirements, for example the keikogi used inkarate. Various physically dangerous sports require protective gear, e.g. for fencing, American football, or ice hockey.
Standardized sportswear may also function as a uniform. In team sports the opposing sides are usually identified by the colors of their clothing, while individual team members can be recognized by a back number on a shirt.