Complex sentence: An All-America team is a hypothetical team, from a given American college sport, composed of outstanding amateur players--those players broadly considered by media and other relevant commentators as the best players, of a specific season, for each team position.
Split into simpler sentences: An All-America team is a hypothetical American sports team composed of outstanding amateur players. These players are broadly considered by media and other relevant commentators as the best players, of a specific season, for each team position.