Just as he was set to begin his sophomore season, Modzelewski moved into the starting lineup after an injury to the Terrapins' Ray Krouse.
In a 1951 game against the University of North Carolina, Modzelewski paced a defense with 12 solo tackles, while the team held the Tar Heels to just 40 yards of offense.
In his two years with the team, Modzelewski showed promise as a rookie, then began having conflicts with Redskins' coach Joe Kuharich in 1954.
As a result, Modzelewski signed with the Calgary Stampeders of the Canadian Football League, ready to play for former Maryland assistant coach Jack Hennemier.
With Modzelewski unhappy, the Redskins traded him to the Pittsburgh Steelers on March 1, 1955, once again reuniting him with brother Ed, a fullback on the team.
The brothers would not play together though, as Ed was traded to the Cleveland Browns as a replacement for retiring Hall of Famer Marion Motley, with whom he won the NFL Championship.
In the NFL Championship game on December 27, he joined an aggressive defense in completely shutting down the Baltimore Colts offense, giving the Browns a 27–0 shutout victory.
However, a season-ending injury to starting quarterback Brian Sipe led to a tailspin that culminated with Gregg's dismissal on December 13.
After first being dismissed with the entire staff one day after the end of the 1979 season, Modzelewski was rehired by Gregg, who had been selected as the Bengals' new head coach.
Despite a 26–21 defeat to the San Francisco 49ers in Super Bowl XVI, the Bengals returned to the post-season the following year, but lost in the first round of the expanded playoff system.