Frostad dethrones Ruud in Olympic freeski big air thriller
Half the 12 finalists scored more than 90.00 in the first run of a remarkable contest, with Frostad leading the way on 95.25, just 0.25 points ahead of Ruud.
Frostad, 23, upped his game still higher in his second run, posting 97.00 to put the rest of the field under intense pressure.
Ruud, next to go, knew he had to go for broke but fell and America's Mac Forehand climbed into second place ahead of the final round.
The competitors were performing aerial tricks off the huge ramp that have never been done in an Olympic final.
Ruud, who won gold in the slopestyle event earlier in the Milan-Cortina Games, came to grief again in his final run, putting him out of contention for a medal.
Forehand and Frostad were the last two athletes to ski.
The American notched an incredible 98.25 to move into the gold medal position with on overall score from his two best runs of 193.25, heaping the pressure on Frostad.
But the Norwegian somehow kept his cool to post 98.50 -- the highest score of the competition -- to claim the gold.
Austria's Matej Svancer took bronze with a score of 191.25.
Events in freestyle skiing and snowboarding scheduled to take place in Livigno earlier on Tuesday were postponed due to heavy snow.
But the big air final went ahead with a minor delay.
The snow was so heavy that staff were using portable snowblowers to remove excess snow and they had to re-mark the blue lines.