I haven't played AC multiplayer since Brotherhood but I don't remember having this many problems using the stun move. I popped in AC3 last night and went through the multiplayer tutorial. It took me through a section where an NPC assassin walked up behind me and I hit X (on 360) to stun him. Seems to make sense to me.
I get into a game and I'll know this guy walking up behind me is obviously my pursuer. I've got my cursor on him so he's highlighted and as soon as he is within range (X pops up above his head) I hit X to stun him. Except I just get an animation of me hitting him, getting blocked and dying. I think they call it an honorable death.
I kept trying to get the hang of how to do it for about two hours last night but I never once stunned anyone. It just isn't clicking. I get stunned all the time point blank in the face but I can't stun anyone else.
Is there something I'm not doing? Do I need to lock on to the character in question before attempting a stun? How does this work?