In 1951, Zeidel entered the NHL as a member of the Detroit Red Wings; in 1953 he began playing for the Chicago Blackhawks. In 1955 he was sent back down to the minors where he remained for thirteen years. That same year, Zeidel suffered a head fracture when he blocked a shot with his skull. It was only because he was ejected from the game that he discovered the fracture, which probably saved his life.
In 1967, Zeidel resumed his career with the NHL as a member of the Philadelphia Flyers where his reputation as a tough guy quickly followed him. He was often a target of other tough players who sought him out to try to rough him up and make a name for themselves.
In March of 1968, after being taunted with anti-semitic remarks by opposing Boston Bruins players, Zeidel became involved in an infamous stick fight with Eddie Shack, which was so bloody that it became one of the NHL's most legendary fights. Due to the fight he earned a four game suspension and a reputation for never backing down.
Zeidel retired at the age of 41 after spending his last two seasons trying to clean up his image as a tough guy by avoiding penalties, to no avail. He had amassed an amazing 3,144 penalty minutes in his 25-year career. According to Zeidel the reason for his toughness was that "I was playing for some coaches and managers who would tell me 'go get him,' so I did."
After he retired he worked for the Flyers in the broadcast booth and as a coach of its alumni team.