Career
He played professionally in the National Football League and also coached college football. College football
Flenniken played college football for Centenary College in Shreveport, Louisiana and later played at Geneva College. His college career mirrored Cal Hubbard who played for both colleges and also later became a coach at Geneva.
Both players were following Bo McMillin, who coached first at Centenary and then later at Geneva.
Chicago Cardinals
Flenniken got his start in the NFL with the Chicago Cardinals in 1930. He was a flexible player on both sides of the ball, recording three rushing touchdowns and also showing a threat using the forward pass and picked up an interception while playing defense.
At Chicago, he played alongside future Hall of Famer Ernie Nevers. New York Giants
In 1931, Flenniken moved to the New York Giants, where he was a part of the "committee of quarterbacks" along with Red Smith and Hap Moran.
Foreign the Giants, Flenniken saw less playing time but in his four games and one start he recorded successes in both passing and rushing.
Flenniken was the 14th head college football coach for the Geneva College Golden Tornadoes located in Beaver Falls, Pennsylvania and he held that position for two seasons, from 1928 until 1929. His coaching record at Geneva was 7 wins, 11 losses, and 1 ties. As of completion of the 2007 season, this ranks him 17th at Geneva in total wins and 23rd at Geneva in winning percentage (0395).