He was selected in the fourth round of the 2004 NFL draft by the Tampa Bay Buccaneers and also played for the Dallas Cowboys and Pittsburgh Steelers.

In his first three seasons at Ohio State, he played behind three-time All-American Mike Doss, primarily in nickel coverage on passing downs.

The first occurred during the 2002 Ohio State-Michigan game, when he intercepted a pass from Michigan quarterback John Navarre during the closing seconds to preserve the 14–9 victory and an undefeated regular season.

In the second half, Allen tackled Miami running back Willis McGahee and delivered a shoulder blow to his left knee.

McGahee had to be helped off the field; he suffered ligament damage and was forced to miss his entire rookie year in the National Football League.

Allen played in every game in his rookie year on special teams but saw increasing time as a safety in the final weeks of the season.

Buccaneers starting safety, Dexter Jackson, had been injured midway through the second quarter with a hamstring strain, and Allen came into the game as a substitute.