Complex sentence: Klassen chose to play his football at SFU because, during the 1970s and 1980s, it was considered the best football school in Canada and has produced over 160 football players who have gone on to play pro football.
Split into simpler sentences: Klassen chose to play his football at SFU because, during the 1970s and 1980s, it was considered the best football school in Canada. It has produced over 160 football players that have gone on to play pro football.