Notably he was a running back for the Detroit Lions in the NFL, and for the Los Angeles Dons in the AAFC where he led the league in numerous offensive categories.

At UCLA Fenenbock played alongside such greats as Kenny Washington, Jackie Robinson, Woody Strode and Burr Baldwin.

As the Lions single wing tailback Fenenbock finished near the top of NFL statistics in a number of categories.

In 1944 Fenenbock starred for the acclaimed El Toro Marine Corps football team In 1945 he returned from military to lead the Detroit Lions to an excellent season.

Fenenbock was the Rockets best player and had a spectacular game in his return to his hometown of Los Angeles to play the Dons.

His small stature, powerful build, and blazing speed meant Fenenbock would always carry the nickname Mighty Mouse.