When the hero is in a fight against seemingly impossible odds, it never occurs to the bad guys to attack the lone hero simultaneously. Instead, they go at it one at a time, allowing the protagonist to handily deal with them one by one.
In real life, all it takes is one well-placed punch or kick to the head for someone to go unconscious. In movies, major characters can last 10-15 minutes being pummeled in the head with fists, bottles, furniture, bats and other weapons and remain unfazed.