Yeah, does anyone have replays where a player gets a decap while one hand is held onto an enemy player's head, without any initial force from that hand? For instance, I clench the enemy's face, and build momentum with my other limbs or my body to rip off the head? What techniques would be good for this?

well
in my opinion, to give Decap easily is very punch the opponent's neck

Mine, Richgar, was one hand on the head, one free, no initial force, only a counter-reaction of mine. The momentum came from him pulling down and my pulling up.

PM me Richgar, I'll show you a legit decap that if I can do 3-6 times a day.

Try contract and extend wrist while you grab it.

I know, the ending was a complete fail on my part, but in this replay I pulled tessh's head off, it was luck but I think its what you were asking for

Fractured hands seem to easily ghost with the right amount of momentum.
When grabbing with them you'll have a big chance of pulling the head off.
Example below.

Wow.. both replays are what I had in mind. In both recent replays, the opponent was grabbed at the back of the neck. In Soulsink's replay, he grabbed the opponent in the lower back of the head. Seems that area around the back of the neck/head is the best spot to decap. I'm going to watch them a bit more.
I wanted to know this so I can have a decapping technique for after I managed a grab on the enemy's face/skull/neck.

Here ya go
It is possible in sp idk about mp though

Yes it is possible
Raise both of your shoulders
contract both pecs
space 3 times
lower shoulders
bam decap i think cause i did that in 3.99 and it worked :P

are you talking about pulling that move out in the beginning, or while you're holding onto the enemy's head? And how many hands on the enemy's head? It only works during the beginning if I also contract my hips and abs while my arms swing down. I can decap using impact force of both arms, but it isn't what I was looking for. I was looking for a move that doesn't use impact force from the hand that is held onto the opponent's head.