At first I though u had a secondary roll in 1 item with stun or something, but u didnt, but after watching the video several times, I don't think u are stunning them. It's just your Provoke taunting them. Just try it with your Crusader alone and see if u get the same visual effect. Even with the stars around their heads, they keep attacking so that's no stun and I can see that effect every time u use Provoke.