Start with what you know:

You wrestled in school.

You played football.

You've beat down a few twerps.

He's not as big or crazy as you, so the last lesson, apply in reverse.

Do slow wrestling with him. Just get on the floor and talk to him while he tries to roll you around.

Then stand against a wall or fence and wrestle with him. Teach him how to get the advantage position and not bore in, but push off, get behind, get past you. I call this goon surfing. Wrestling with you, who he cannot overpower, as you speak with him calmly, will help him relax and seek the advantage position. Mario Sperry, "the Zen Machine" a top BJJ/MMA pioneer recommended doing Jiu Jitsu against a vertical surface, not on the floor. You get your head kicked in by third parties on the floor.

Next go to boxing. I will send you a copy of The Punishing Art. For him, all he needs is a pair of boxing gloves. Let him hit your palms without bringing them to him. Hold your hands steady and resist the temptation to meet his punches. Alternately, place your free hand on his head and sometimes shoulder, letting him know that his goal is to hit both of your hands without you touching him with either. You might not feel confident in your knowledge of boxing. But, your wrestling ability is a better governor for his self-defense boxing ability than most references. The danger to a boxer, in a self-defense setting, is getting grabbed by some big redneck out of the Utah wilderness.

As far as coaching him in boxing, some of the best boxing coaches never boxed. You just have to understand what you are seeing. You don't have to be able to do it.

Good luck and address any specific questions to me and I'll answer them.