I think it should be a muzzle thump with something along these lines for damage.

All hits should cause blury vision, low stamina and maybe wobble. Hits must be consecutively applied within no more than 2 seconds of each other.

1st hit Body: Stuns the person for 1 second

2nd hit Body: Stuns the person for 3 seconds.

3rd hit Body: Knocks the person down and stuns them for 10 seconds.

Head hits:
1st hit head: Stuns person for 3 seconds.

2nd hit head: Stuns person for 6 seconds and knocks them down.

3rd hit head: Knocks the person out

4th hit head: Kills