Neck curls. Just search alphadestiny's videos about neck training. You could do it with a plate on your head or just buy a neck-harness like pic related and do it that way.
Neck exercises
Kevin Lopez
John Taylor
doesn't this shit snap your neck?
William Sanchez
who dis
Ian Baker
That's half the fun
Ian Myers
I'm training my neck with it and haven't felt any pain from it. Obviously you're gonna start with light weight or bodyweight neck-curls. Just do high reps and sets with a weight you can handle and you should be fine.
Camden Hill
...
Jaxon Price
George Fisher has only done unweighted headbanging for his humongous neck so I'd guess weighted headbangs if you want faster gains. make sure to put that harness tight though or someone's going to get hurt.
Aaron King
his neck makes him look like an autismo
Austin Evans
Would strengthening neck muscles help you take a punch