ace: he would probably win due to his strength and size advantage, but you should challenge him to a fistfight anyway, just on the off chance that you win. also, he is easy to confuse if you just wear different clothes. if you do that, then you would win the fistfight handily
snake: if you’re punching him for no reason, you would probably win since he can’t fucking see you. if you’re punching him after hurting his sister in any way, you would lose the fist fight within 0.005 seconds
santa: has a six pack and a secret gun and is very angry. you would not win in a fistfight
clover: might be small, but is full of unbridled rage at all times and will immediately sock you in the jaw without thinking first. you would not win in a fistfight
junpei: hands down, you would win a fistfight against junpei, as he is a weak and scrawny nerd. you wouldnt even have to fight him, you can just tie his shoelaces together when he’s not looking
akane: though you would almost definitely win in a fistfight against her if you’re in a timeline where she has not fought you before, she will probably just jump to another timeline after beating you and use all your tactics against you. you would probably not win in a fist fight, unless you expose her to fire, in which case you would still probably not win in the end even if you win the fistfight because she will trap you on a boat and threaten to kill you
seven: he’s a fucking cop. you would not win in a fistfight
lotus: though her big bazongas might seem to get in the way, she is actually angry constantly and is ready to punch out anyone, at any time, for any reason, especially if you threaten her. you would not win in a fistfight
9th man: he dies if you look at him wrong. you win the fistfight with little to no effort