Never heard of an increase in motor skills during a violent encounter other than maybe when receiving an optimal level of adrenaline... Not to say it isn't possible, just never thought of it I guess.
I'd imagine that would come only with a very high level of training.
An episode of Fight Science (probably the best episode of one of the worst martial arts shows ever produced), looked at putting ex-spec ops guys into stressful situations, and then tested them on combat skills against an earlier baseline. They all performed better after being "stressed."
The idiot scientists conducting the test kept mumbling that there was no scientific explanation for the results.
The ex-SEAL even told them he was just doing what he was trained to do when he raised his core body temperature after being submerged in ice cold water for an hour.
I couldn't do anything but laugh and shake my head.