In the grand scheme of things, the astronauts have already won.

The astronauts may not have weapons, but when they construct that rudimentary cannon, watch out Caveman!

If you're telling me Chuck Yeager needs weapons to show some motherfucker who lives in a cave which end is up, you must be shit-jiving!

Unless you are placing the fight in a total vacuum without environmental or circumstancial effects, the astronaut will always win because his mind is more suited to using incidentals.
Besides, in a vacuum they are both screwed.
Unless...it's the total vacuum that is space, in which case I'm still right.

As much as I'd be rooting for the astronauts, there's this tiny problem called muscular atrophy that happens when you spend too much time in low-g. That, and your bone mass drops. Compare this to a bunch of cavemen, who are of necessity living a very physical life, y'know, dragging home mammoths for dinner and shit like that. This one should be a no-brainer, kids.

Kirk vs the Lizard Guy, baby.

*hangs head shamefully*
The Gorn. Yeah. I know its name. *sigh* I even know that that's not a personal name, but a race.
I'm such a geek. *bursts into tears*

Chuck Yeager vs. fucking Og, man, no question.

Muscle atrophy, sure. Unless they're astronauts prepping or what-have-you. They're in EXCELLENT damn shape most of the year. And even old Aldrin, I think it was, can knock a young, athletic fellow straight on his damn ASS in one blow. I read about it in the paper. You ought to be able to google it. Second, think about this: Medieval Euros were almost a foot shorter than us. And they had a slightly better diet than cavemen. Now, cavemen may be damn HARD mothers, but the astronaut is probably over a foot taller, heavily trained (in survival techniques, as well), inevitably smarter, and has military martial arts at his disposal. So, unless he's at that point where he has to be carried out of the pod, he is going to Kick Ass Hard.

I've read about how astronauts (at least in the past) are trained. They're usually military. They usually have to be super-proficient, physically as well as mentally.

I think it is funny that while (currently) the votes are even, all but one comment is talking about how astronauts would kick caveman ass.

My vote was for astronauts, mostly for the military background and general fitness level. Thinking about it though, caveman had some pretty thick skulls. It may take a few dozen punches and kicks to their head for the astronauts to win. Considering the language barrier, it would be likely that a caveman wouldn't understand that it was not to the death, so I could see the caveman at least trying harder, and the astronaut to actually need to make the caveman fall unconcious. On the other hand, I could see an astronaut first breaking the shin of the caveman, followed up by a few throat and temple punches. Yeah, astronaut wins.

caveman had some pretty thick skulls

But astronauts have helmets. :-)

I think that most would prefer to not be wearing the helmets or suits during the fight; they would slow them down.

Besides, the helmets won't fit right without the full astro-suit, and that's pretty darn heavy. And those thrusters? Probably pretty useless on earth.

On second thought, if they did show up in their EVA suits, it'd probably scare the cavemen enough to avoid the fight entirely.

Hmm. Of course, those Tarzan-style outfits on grubby little cavemen might frighten the astronauts. Especially the Ivy-Leaguers.

Maybe it would come out in a tie.

moreover, any astronaut is going to be steeped in the rich, millenia-old tradition of subterfuge and trickery and betrayal (our beloved human heritage), the contents of which are simply inaccessible to the common caveman.

take away the smarts, the helmet, the martial arts and the basic training, and astronaut was still raised by his momma to be a backstabbing motherfucker. the caveman can still turn on you, but our guile has been raised to an art.