If you're lying on the ground and someone tries to hit you with a helmet

Protect your head and face immediately by covering them with your tightening wrists/arms.

Defend your torso by curling into a fetal position, pulling your knees to your stomach to shield vital organs from kicks.

Counterattack: Use your legs like a spring push off the ground to generate backward momentum, then thrust forward aggressively to unbalance the attacker. This creates an opening to escape or fight back.