Fling (one's) head back informal verb phrase
Move one's head backwards quickly and immediately
I flung my head back to avoid his blow.
He flung his head back to avoid the hit.
She flung her head back in disbelief.
To move quickly up and down and from side to side, typically in an attempt to avoid hitting or being hit by something
To move in a slow and unconcerned manner.
To hit, attack or strike someone in a way that causes serious injury or death
To head to something or someone quickly and directly.
The verb "fling" should be conjugated according to its tense.