Playing rec ball a month or two ago, I committed the act. I was providing cover from a corner bunker as two teammates worked their way outside the main perimeter of bunkers. My hand somehow slipped, and wouldn't you know that the single errant ball smacks my buddy in the back of the dome with a nice 'thwack!' He reached back to check, and his head was amazingly clean. I felt like an idiot, but at least it somehow bounced and nobody had to go out.
Except... when he took off his mask in the dead zone after the game, we found that the cracked but mostly intact paintball shell had tucked itself neatly behind his ear, lodged up under the mask band with a blob of paint, so clean that with the mask on none of us could tell it had actually broken.