My gladiator:

Level 26 Theatrics
Called Shot - 5
Knockout - 6

Currently my Fight Strategy is Middle Activity Level, Middle Blood Lust, and only aiming for the Head. This has been my Strategy for over a week now.

So far I've not seen Knockout do anything at all.

I can see a few possibilities...
- I'm doing something wrong.
- I'm very unlucky.
- This High level skill is not working as intended.
- This High level skill is working as intended but in my opinion not worth the point or effort to take.

-Lance