Way back in the 1970s the North American Hockey League had a hockey club in Pennsylvania called the Johnstown Jets. They were a tough bunch of boys. Three real brothers - Jeff, Steve, and Jack Carlson - all had long hair, thick glasses, and consecutive sweater numbers. Dave "Killer" Hanson was a guy that opposing players tried to avoid on the ice. Another team mate, Ned Dowd, had a sister who was a screen writer named Nancy. He told her stories about the Jets' outrageous exploits both on and off the ice.
Nancy Dowd wrote Slap Shot but actors who could skate well enough to portray professional hockey players proved hard to come by. Nancy and Ned suggested that director, George Roy Hill, give the Carlson Brothers and Dave Hanson a chance. After all, they really didn't have to act - they were "playing" themselves.
The filming was scheduled to take place in the off season, but brother Jack got called up because Edmonton made the playoffs. Dave Hanson took Jack's place and Jerry Houser was cast to play Dave's original role, "Dave 'Killer' Carlson."
It was a fun summer job, but no one ever dreamed it would be more than that. All the guys went on to play professional hockey (Jeff - 11 years, Steve - 14 years, Dave - 10 years, and jack - 12 years)