Emo
Depends on how you define "possible"---that some people have done so is probably accurate...that any given person can so is a HIGHLY problematic.
The variables involved are legion, how good is the swordsmen how good is the un-armed guy, what is the actual siuation, how close are they are, are they in armor etc.
Percentage wise the old-timers often figured that even armed men had about 1 chance out of 3 of getting out of a sword (weapon) fight alive and more or less with all your limbs intact....consider how much LOWER a percentage you would have with no weapon.
IMO in "theory" its possible....but in "practice" the chances are "slim" and "none."
Of course if you have no other choice--"slim and none" starts looking better.