An overhand right or left is a crude inefficient punch. One has just as much chance of breaking their thumb or hand as they do knocking someone out with it. Its a natural movement and so most "amateurs" use it because it "feels-good" when winding your shoulder as fast as you can and making contact. Its as natural as throwing a baseball. Problem is contact is made usually with the "bad unstable" part of the hand (from the thumb to the first knuckle) anything from sprained wrists to broken hands are more frequent. Boxers don't use it or try not to for some of those reasons (but the natural motion is hard to shake). IAnd believe it or not, there's more power from a straight right/left with everything "lined-up" torque-wise from the torso, to the shoulder, down the arm to the straight wrist into the main 1,2 and 3rd knuckles solid like a hammer. That's why boxers focus on that more, more efficient, more compact, gets to the target faster, and harder to see coming, especially when you can hide it with a jab in the opponents face first.
