you can't compare the recoil on a crossbow to the impact, they are completely different forces acting on completely different objects. the bow action is created by release of tension to start, which is a totally new ball of wax, as the parts which brace the machine are already by default holding in place the maximum amount of force that can be generated - it's all downhill from the draw weight. Because of this bracing, most bow weapons move forwards when fired, not back, and only with a fraction of the force as most of the actions within the mechanism balance each other out. It's not unrelated to the force of the arrow in flight, but it's different.
there's no way to know the draw weight or bolt weight on this nonsensical machine he's firing, so there's no way to tell the force of the bolt. However, we can assume that the bolt has enough force behind it to penetrate the skull, which is enough to knock anybody's head back.
"you can't compare the recoil on a crossbow to the impact, they are completely different forces acting on completely different objects.
.....
It's not unrelated to the force of the arrow in flight, but it's different"Contradictory much? Those mechanisms you listed that mostly nullify the recoil
account for the mass I mentioned exerting the oppositional force. The thrust of the bolt that they are opposing is the SAME force—ignoring air drag—that the target's head is absorbing.
That is how they are related.
Also, we do NOT assume that the force of the bolt's impact is enough to penetrate that skull; we
know that as a given of the situation. The assumption is the knockback, which we base on our approximation of the head's mass, it's fixation to it's initial position, and the bolt's velocity.
Also, let it be known that when the bolt is airborne, the only forces acting upon it are downward (gravity) and backward (air drag). The idea that something needs a lingering force to continue carrying it along in a certain direction is archaic and defunct.
Also, let's get back on topic shall we?

Sorry, `Rob.
In addition to the target's arms being drawn further back, I agree with Kcilc that there should be no bolt IN the crossbow. Also the lighting seems inconsistent to me on the target.... his face is lit from the front, but his cape is lit from the back.