Whose strength would leave him if his head were shaved?

Answer: Samson

Samson revealed he was a Nazirite from birth: "If I am shaved, my strength will leave me."

“Samson told her all that was in his heart: “My hair has never been cut, because I have been a Nazirite to God from my mother’s womb. If I am shaved, my strength will leave me, and I will become as weak as any other man.””— Judges 16:17 (BSB)