The robber punched my helmet, what probably fractured in his hand

[Markscarinci]

I was riding my bicycle toward this punk on the sidewalk and he stepped into my path and wanted to know my teeth out so I ducked at the last second and he punched my helmet square on!  I heard three quick distinct cracks  with the last one the loudest and then a loud scream. I kept on going. So in all probability, what likely fractured?

[CHIN_C]

Closed fist or punch injuries can cause fractures of the 5th metacarpal neck (Boxer’s fracture).

[Markscarinci]

Thank you Chin_c
This gives me peace of mind