Yikes.
Looks like this is the end of an accident chain. Somehow the roller furler got fouled. The genoa sheets are tangled from flogging. Two guys on the bow working on that. Helmsman entirely distracted by events and probably issuing orders . Guy on the boom was put there as a temp preventer, which is common enough. After all, racing you're pulling the strings constantly, gots lots of crew, and in slop one of them can hold out the boom.
But the guy on the boom is inexperienced. We all know that in that particular posture you have no leverage at all. Need to anticipate the boat at least rolling, maybe even jibing.
Maneuvering the boat to picking him up must've been a real fire drill, given the mess they were in already.
But it is the fellow in the companionway who is the lucky one, and would never have seen the skull fracture coming.
Race skippers push crews and gear hard, risking collision and catastrophic rig failures. In my opinion, all injuries to crew are the skipper's fault.