Shading is really good! I do have some constructive criticism though....
First of all, I think the characters should have hair, but if you like drawing bald dudes, that's totally okay!
The blue dude should look like he's being punched, not that he looks like the red dude is just tilting his head up. Try tilting the blue dude towards the air! Also you can add some branding on the trunks or make the waist bands bigger. Otherwise, cool art! :D