Complex sentence: He won the Trans-Am championship in both 1972 and 1976 and was the 1972 Can-Am champion, substituting for the injured Mark Donohue in Penske Racing's Porsche 917/10, causing the racing press to dub Follmer "George Am".
Split into simpler sentences: He won the Trans-Am championship in both 1972 and 1976. In 1972, Follmer was the Can-Am champion, substituting for the injured Mark Donohue in Penske Racing's Porsche 917/10, causing the racing press to dub Follmer "George Am".