What does your trained fighter want to happen? Capture? Evade? Knock untrained guy out? Kill the guy?
Different responses to each sitch, and each mode of fight-training. I'm not a trained fighter, but I suppose if I was in a sitch where I was fighting someone, it would be a serious situation for me, so I would try to do damage, as I would be in fear of my life. I'd try to stay out of range, assess area for weapons (like a gardening tool, say, or heavy/hot/toxic things to throw at him, just thinking about a home attack.)
This assumes I can't get the fuck outta there, because running is (most often) an untrained person's best option. After getting mugged in my apartment, and pulling a knife on the guy (instead of just quietly holding onto it and stabbing him when he dragged me through the kitchen to the bedroom, which is what I should have done), I decided that I will never threaten anyone with a weapon I am not an expert in. I should have thrown a piece of furniture or two through the windows to attract attention. That is Plan #1 for me if I ever am attacked at a home again. I have lots of back-up plans, too.
Can't get out, if you can get a weapon, don't advertise it. Hide it, and wait.
If you can't get a weapon, Suzi and lisah are right. I'd try to get him in the knees, fuck up his balance, cause some pain. I'd go for the throat or eyes; I'm short and most people telegraph a kick to the balls, most guys expect it, and most protect against it more diligently. Plus, the danger of him grabbing my leg if I'm not fast enough. Rape subjects are advised to try not to get on the floor, but I have some crazy lower strength, so I could do some damage (face, kidneys, maybe ball, throat, face) there, and get him off of me. I'd take some punishment though.
And then try to use speed, and stay mostly out of his way. Try to get some knee damage, ankles; trip him up (cause I'm short)and wait for him to falter to use a weapon on him and run, or punch or kick him in the trachea and run.
I'd get kinda beat up; I am pretty totally untrained. But I'd also be pissed and I wouldn't give up.
You're probably thinking of a different kind of fight than untrained chubby 5'4" girl vs. dude, but I think my reactions would be similar were I trained, although I obviously have less -- well, almost no -- expertise and technique. And strength.
But I think I'd have a chance. If I'm smart. And I know from experience (one mugging, okay, not that bad, BUT) that I DON'T freeze up, that I still think and plan. My plan wasn't PERFECT, but I'd never been attacked before. It worked, that's all that counts. I got a few bruises, my face beat up, but I realize my brain is my best weapon -- I bluffed him out of raping me -- he didn't kill me or beat me anymore and he left.
And I know that I act if anything happens. And I kinda actually strategize under stress. I wish I hadn't been mugged, but in a way, it's one of the most valuable lessons I've ever had, and I kinda don't regret it, given the circumstances.
Wow, I got distracted. I gotta fight someone now (seriously) using words this time.
Morning!