Firstly. On reading this, I was just a bit 'meh'.
But that aside.
The first bit, before the fight, sounds fine.
Second bit, when the creature rushes him, I don't think it really enhances the fight. Rather I would just have him come in swinging the axe, then the sergeant just makes a matrix style dodge, barely making it, maybe even having the axe nick some of this hair. Then we see the chain and weight swinging.
Nothing wrong with the knee and roundhouse.
When the next arrow comes, just from my own POV, I like the idea that he uses his chain to hit the bolt into the air. Then as he is preparing his next attack it falls down just in front of him, flashbang attached. It goes off, stunning him. Then he takes the bolt through the leg, grounding him.
He tries to counterattack but gets it tangled in the tree because he still can't see properly.
Another bolt flies and pins his foot to the ground. Immobilized the monster jumps towards him, massive overarm swing. Without looking the sarge flicks the twin out of his other sleeve, turns it into a scythe, and beheads the creature. Then narrowly avoids the axe as it continues past him.
He then proceeds to pull the bolt from his leg and foot while still seeing spots in front of his eyes.
Though, to be honest, I find it weird that here you have a monster that stands 50% again as tall as a human, is super fast, super strong, and super tough. Wields a giant axe that has been modified to also be a crossbow. It also has grenades, and is rather acrobatic to boot. And here we are fighting it with a chain...