Armstrong was a graduate of the University of Western Michigan in 1989 but had not been drafted by any NHL team. The Philadelphia Flyers signed him as a free agent, and he was assigned to Hershey, where he played all of the next three years with one exception. During the 1990-91 season he was called up by the Flyers for a single game, and wearing number 58 managed to register an assist.
The impression he made, however, was not enough. He was sent back down to the AHL team, and for the next eight years played in the minors without another game in the NHL. His contract expired with the Flyers and he signed as a free agent with New Jersey, but the Devils had no use for him on their Cup-quality teams.
In 1998, he retired to become an assistant coach with Providence in the AHL, staying in hockey and hoping for better fortune behind the bench than on it.