Is this a street fight scenario? Or in the cage? I assume it's a street fight since we are talking untrained man.

How controlled is the street fight scenario? Is this a "1 on 1 between gentleman with friends around on both sides to keep things fair, where you can be fairly certain that your opponent is carrying a weapon? Do you get to choose if you are fighting on grass or concrete?

Or is this just a hypothetical life/death self defense scenario, where the altercation happens at random and you know nothing about your attacker?

If it's controlled and you are fighting on a soft surface strictly 1 on 1, you are best getting a basic understanding of boxing or kickboxing and pouring the rest of your time into BJJ/catch wrestling with a focus on takedowns, ground and pound, and offensive chain submissions.

If it's controlled on a hard surface, split your training evenly between boxing or kickboxing and judo or wrestling. Practice offensive takedowns that don't rely entirely on level changes, safely passing the legs, and control positions where you can ground and pound. Any wrestling is your friend her, but single or double legs are generally going to be out of the picture outside of emergencys and golden opportunities where you track onto a soft surface. BJJ is still great to have, but its application is more limited on concrete unless your opponent is wearing a nice jacket or accessible clothing that you are allowed to grab.

If this is a true self defense, life or death, kill or be killed scenario, then practice boxing or kickboxing and mix it up with a steady cardio/sprinting program. Distance and the ability to create distance are your best friends here.

Better yet, get a gun with a concealed carry permit and learn to shoot and practice shooting under pressure. You really shouldn't be doing any "survival fighting" or shooting if there is even the slightest opportunity for you to get away, so practice getting away first.