Kanitah doesn't have any control over the legs, he's exerting pressure from outside, literally it's just Fury's own hooking position that would limit his ability to escape, which means he's free unless Kanitah has the ability to stop him from flying out of the grip because Fury's feet are hooked angling downwards and outside, flying up would allow them to easily escape (especially as his feet would just naturally turn, abandoning the hook, when he did this.) (I'm not sure there's any physical way Kanitah could stop him, other than trying to lift his legs up and catch Fury like a crab or something.) But it's highly unlikely Kanitah would have chance to react to Fury suddenly not being there in that way, the weakside to exerting a lot of strength to an action (like forcing open a door with shoulder barges for example) is that when someone suddenly abandons all their resistance, your momentum carries you with an unexpected lurch.