He was an early proponent of the forward pass after the revolutionary play was added to an extensive list of regulations to college football in 1906.

By 1911 when most of the pass restrictions were lifted, Mahrt debuted as regular back on St. Mary’s Institute’s (now the University of Dayton) varsity football team.

Mahrt discovered that spinning the throw of the ball increased accuracy and distance, establishing an aerial offense against such teams as Xavier University and Otterbein College.

In 1913 Mahrt switched to the St. Mary’s Cadets, the precursor of the future Dayton Triangles, he was also named the team's captain.

In 1920, Al led all passers in the American Professional Football Association (renamed the NFL in 1922), completing 28 aerials for 591 yards.