True story that happened to me 17 years ago, this is before I did any martial arts.
Got into a fight after a party against two people - that is to say they jumped me.
Fight goes to the ground with me on the bottom. One guy gets on top and starts flailing away and the other guy starts kicking.
By some instinct I grabbed the guy on top and pulled him close. In some sort of shitty untrained instinctive gaurd. The person kept on punching and beating my sides, but the other guy couldn't do anything without hitting his friend.
I was traumatized at the time however in retrospect I came out of it with only some lumps and bruises and nothing worse than I have experienced in years of MA training.
Lessons I learned.
1) Fight's go to the ground sometimes no matter what.
2) Knowing what to do from the bottom is not just for trying to submit someone but seriously important in defending yourself. My shitty instinctive guard kept me from getting a real beating.
Ground fighting / grappling is not just about slick submissions but also how to survive and reverse the worst postions.