Crushing fist only activating when name locking monster

Using Crushing Fist on R2 + Square and I noticed sometimes the skill wont work even though I had the indicator to say its usable. I did some testing and it only activates if Im name locking a monster (or hovering whatever you want to call it when an enemys health bar is shown at the top of the UI). Given its a slam skill this seems to be working incorrectly as I should be able to use it once Ive blocked, slamming in front of my character.

Thanks