The flail is a _very_ dangerous weapon, and nearly as dangerous to the user as it is to the recipient. Large flails were definately heavier and clumsier than a sword, and would be 'spun up' for a moment or two before wading into battle. Shorter ones that could actually be 'struck' with have a bit of physics, that part about conservation of momentum, and angular momentum, that speeds them up tremendously when the bend over a shield. Much more power than a somple axe or sword strike.
Incidentally, these facts, plus the idea of fighting with a chain/rope swinging around entangling things, have resulted in it being one of a few weapons not allowed in SCA combat. I wouldn't want to take part in any kind of non-scripted re-enactment involving a flail unless it were padded quite nicely... Just too easy to be malicious with...
Stryver