The Question
The flail is the parry-killer, and it is the one weapon the guilds make with a kind of malice. The head is a ball or a flanged star on a chain, and the chain is the whole point: the head does not go where the parry expects it. The parry goes to the haft. The head goes to the face.
The flail is the question the world asks every parry: what if the thing you are meeting is not the thing you think you are meeting? The answer is always the same, and it is not a good one.
In the Hand
One hand, usually — the flail is the weapon of the fighter who keeps the other free, because the flail is the weapon of the fighter who has already decided the argument is over. It is the ranged band's cousin: the head flies, the head finds, and the head lands. It is the answer to the long sword's parry, and the question the long sword has never learned to answer.
"A flail is a promise you make with your other hand — the hand that is not holding it." — guild master, The Company