Collella was drafted by the National Football League's Detroit Lions in 1942, and played two seasons for the team. The Cleveland Rams acquired him in 1944. He played as a halfback and punter for the Rams, who won the NFL championship in 1945. The Cleveland Browns, a new team under formation in the All-America Football Conference, signed Colella soon after the 1945 season ended. He was among five players who joined the Browns when the Rams moved to Los Angeles before the 1946 season; the others were Chet Adams, Don Greenwood, Mike Scarry and Gaylon Smith.