A skeleton was painted on the back of his helmet.

I even had his name put on the back of my helmet.

A stone bounced off the back of his helmet.

Marko brought his ax down once more on the back of the falling chief's helmet.

"Did you have eyes in the back of your helmet?"

The bullet hole in the back of his helmet told Kevin all he needed to know.

Then something tapped the back of her helmet, and a new voice spoke in her ear.

He swung his own blade hard against the back of Guy's helmet.

I helped him to open the control valve on the back of his helmet.

Something banged at the back of his helmet, just a tap, really, but it startled him as if he'd been shot.