In the third period of a game against the Rangers two weeks ago, Phoenix Coyotes goaltender Jason LaBarbera made a big save but was slow to rise from the ice, seemingly injured.

On the Phoenix bench, before thousands of raucous Madison Square Garden fans, reality struck Tom Fenton like a blindside hit.

“Immediately it went through my head: God, I might actually be going into this thing,” he said.

He didn’t. But that night Fenton, by day a Manhattanville College graduate student, was an emergency backup goalie, or EBUG, one of a subspecies of Average Joe hockey players called upon to drop everything to fill a roster spot when a professional goalie is injured or ill.

EBUGs have become something of a staple of minor league hockey and occasionally find their way onto an N.H.L. bench for an evening. One thing they all have in common is they are not expected to play, and usually they do not. In fact, it is not believed that an EBUG has played in an N.H.L. game since the league mandated after the 1965-66 season that teams dress two goaltenders, the result of complaints that backup “house goalies” provided by the home team were not up to the task. Under the league’s collective bargaining agreement with the players union, teams may sign an amateur player to a one-game contract in an emergency.