Actually, I've always wondered that myself. What happens if he wins? But the fistfights are so ridiculously easy in the game that I couldn't lose even if I tried to. 
If you get beaten, then he gets selected for the cockatrice mission. Needless to say, you have to go some time after him and find his dead body.
two things, yes he can be beat I have never been beaten by him, when fighting once you left click and the fist symbol comes up wait for the witcher to land a punch then tap the right click and left click again keep doing this over and over and you will wipe up the floor with everyone you fight, next thing there are 2 talents for fist fighting you will need them
As all others fistfighters ingame (up to Act III, didn't went further on that game), I found the ultimate trick to win the fights :quickly, but not too much, press Right - Click, Left - Click, do that,repeat, again and again. Opponnent won't even touch you once (most of time).(planning to make some video to illustrate)By the way : your potions work too for fistfight. You can't use'em during the fight, but you can drink one (or many) before. Thunderbolt does it, adds a bit to your damage, as Shrike will cause Pain if your opponent comes to hit you. Funny then to chain a couple of jabs on some crippled - in pain fistfighter ! Not useless, because you usually do a lot less damage than your opponents, that seems to be at least level 50+ with a lot of talents in Strenght ^^Last point : only fight I lost was because I was "pushed out" of fighting area (I guess) because of that damn fistfighter that we can't challenge and wich is standing in the middle of the fistfighter's corners (Act II, Act III). He stands in the middle of there, and well, like a wall between you and your opponent you can guess it complicates things.
yea it helps kknowing how to block but i beat him even tho i forgot howZanderat said: