Generally speaking, fighting is a losing game. Instead of gaining strength by fighting others, most players in NEO Scavenger will gradually be whittled down by each fight. So as a rule, retreat and avoidance are usually the best bet. (There may be changes in the future that improve characters as a result of a fight, but nothing like that exists now.)
"Strong," "Tough," and "Melee/Ranged" are three skills that really dominate a fight. Having 2-3 of those and a matching weapon can really improve your chances. Similarly, enemies with those skills make harder targets (though only the first two are known to you in a fight.)
"Feeble" and "Frail" are pretty serious handicaps in a fight, and are also visible on others.
The weapon you're using will make a difference, though without skills to back it up, not as much. I'd sooner run from a strong/tough dude with fists than an average dude with a meat cleaver.
The terrain rating will affect your ability to move without tripping, so that can be a factor too. Retreating won't help if you're constantly falling on treacherous slabs of rubble and rebar. One exception is when a creature has "Athletic," which allows movement over rougher terrain with less chance of tripping.
Lastly, tactics matter. With or without any of the above on you or the opponent, the right move at the right time makes a difference. Knowing when to parry or dodge vs. attack, knowing how to control range, and being able to take advantage of changing conditions (like a fallen or stunned enemy) will make a bigger difference than stats alone.
In conclusion, you should probably run :) But the above tips will improve your odds if you have to fight.