Yowsers! That Hurts!
This is what happens to my bald head far too often. The worst has come here in Guatemala where some families use old, rusty barbed wire for clotheslines. They stand at a height of 5'6", whereas I stand at a towering 5'10". Usually, wearing a cap helps cushion a blow, but not every time. Another bad deal is low hanging roofs made of sheet metal (also often old and rusty).
This time it was my own fault, I jumped out of the driver seat in the van and whacked my head really hard. I took my cap off and then rubbed the scraped skin off of the inside of the cap.