The first thing that jumps out to me is the lack of gesture in the pose, it's very stiff. I don't know if it's a stylistic thing, but the lack of gesture takes away any feeling of force. Also, the left arm and finger are creating a tangent with the border of the image and the pants. The head also feels like it lacks structure, and the right arm is too short as mentioned by others. I did a quick sketch to show you what I mean, I hope it helps :)

Well done! The first thing that jumped out at me is the right arm. I know it's foreshortened, but even taking that into account, there's some proportional issues. If the upper arm is away from us, which would explain why it's so short, we shouldn't be able to see the elbow. If we can see the elbow, then the upper arm shouldn't be this short. If the right shoulder is retracted, another reason why the upper arm is so short, then we shouldn't see the shoulder. Also the hand position looks very uncomfortable. I tried to do this pose myself and it's nearly impossible. His head/face looks too small for the size of the neck. Then there's the question of what's the focal point? I feel like it should be the face because of the blood and his interesting expression. But what's presented is his left leg and foot, which doesn't seem to be doing anything. His left foot is very relaxed. Also, is he jumping in the air or is he kneeling on the floor? If the former, the right leg makes him look like he's kneeling on the floor, which is not a very powerful position. Your rendering is really good though, very polished.

Wow that looks really amazing!!! Since this looks very professional I gonna go for a very detailed feedback :) I think the pose looks a little bit like you don't know exactly where to go. I did Muay Thai fighting for a few years and with these fighting poses there is always a very defined direction in which the force you apply go to. The base is always very solid (keep your arms and legs in your basic position to not loose balance) and only to block or attack you get a strong force in the diection you want to hit your opponent. In your pose the force of the knee is going to the front right and the hip of the character is twisted to the right so the hips direction is to the left. But in Muay Thai and MMA the force always comes from the hip and the shoulders. The arms and legs are more like an extension but the punch/kick comes always from the shoulder/hip. So I would adcive to either put the left leg in a position there it is pointed to the left (like the direction of the hip in your drawing) or to adjust the hip and the torso. Since the Torso and Hip/Leg direction go all over the place, he seems very unsolid and in a fight he would really fast loose his balance and be a nice prey :)