Concussion Online
You will firstly have the right to choose a quick tutorial mode to learn some basic controls ( if you want to get into the game at once, that's fine but the training is highly recommendation so the fight will be much more fantastic). Don't click Concussion online if you don't want to be addicted. This is a fighting game with simple design - just two stickman fighting but there are so many movements that you will feel interested. Try one time and you will not get out.
In case you don't want to be trained, here are the game controls:
W,A,S,D: move
J: kick
K: punch
L: extra punch
L+D/A: high kick
L+S: power of hand