Those Colorado Rockies teams were not very good. They lost a lot more games than they won. Cooper thought he had his ticket out of there in 1982 when he was traded to Edmonton for Stan Weir. The chance to play with an Edmonton Oilers team that was soon to emerge as one of the NHL's all time best would have been amazing for Cooper, but he arrived with a shoulder injury that the Rockies never disclosed to the Oilers when the trade was made. The trade was reversed in the summer time.
That shoulder injury cost Cooper the entire 1982-83 season and ultimately his career. He never returned to the NHL ice, and only briefly in the minor leagues.