ok so this is theoretically possible, but in order for it to happen some circumstances needs to be in place:
1. use a swing attack in a predictable manner against an unarmed opponent.. (If he would turn into the swing, feint a bit, hold the swing or use some other trickery, it would be excessively difficult to chamber it.)
2. If he would in stead use a thrust or overhead in an easily chamberable manner, the only consequence would be knockdown.
3. How many players chamber a lot in combat anyway? I can recall 1 and thats Darkfox. Combat chambering is already very risky and difficult, more so doing it unarmed...
4. The attacker can clearly see the opponent is unarmed, and thus could be expecting a chamber. He needs to make his preparations.
5. If besides this, some archer manages to make him drop the weapon, he can just pick it up again, if the archer isn't faster..
6. If someone manages to pull off these kinds of chambers, well.. Kudos. They are good players and get rewarded for being that.