Penn State's head coach went for it on 4th-and-4 in his own territory with seven minutes left in a close game.
Allar hasn't been dazzling on the road thus far. His struggles continued on Saturday.
The Nittany Lions' consistent failure to convert on third down wound up costing them one of the biggest games of the James Franklin era.
Nelson missed the majority of the game against Northwestern and was absent against UMass.
The matchup between the two top-10 teams will be televised on FOX.
Tanner Palocsik scored deep in the third period to give Penn State the lead and the win at Pegula Ice Arena Friday night.
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