I just googled it because I've never heard of it before... it's pretty crazy.

Apparently, the wrestlers cut themselves on their scalp / forehead some time into a match to make the match look more intense, with the blood from their head mixing with sweat and dripping down...

A 17 year old kid was even hospitalized due to blood loss from it.

https://en.m.wikipedia.org/wiki/Blading_(professional_wrestl...