When the hero/heroine punches the baddy in the face/jaw/head, and sends them FLYING backwards dozens of feet. First of all, to just LIFT someone up off the ground with a head punch (assuming your average movie bad-guy 200 pounds or more) requires a LOT of force, let alone to PROPEL them backwards. I'm not talking about stumbling backwards and they fall down, I'm talking about how the body goes flying through the air.
It's just NOT going to happen like that with a human being, even if the hero/heroine is a bulked up fighter / power lifter / martial arts expert / Special Forces / whatever.
And when the hero/heroine has SUPER strength, then a blow to the head with significant force to hurl the entire body backwards dozens of feet would ALSO be strong enough to first either:
1) Tear the jaw/skull segment loose from the rest of the head, therefore just making a big splatter mess, while the nearly decapitated body falls backwards, or...
2) Completely decapitate the body