Perhaps I am mistaken but it seems like a sword, axe, spear or hammer would make better melee weapons than the flail on a battlefield. In the crush of close combat it does not seem feasible to swing a flail.
Was the flail something more likely to be used to a tournament or duel than on a battlefield?
If it was used on a battlefield how were they able to wield it successful?
Or is this a case where the actual use of a flail has been incorrectly portrayed in TV/Film?
Well, if you're thinking that only the military flail was used in combat, you are in for a treat.
There are tons of instances of farmers using their flails to attack and kill groups of soldiers. Why? Well, the soldiers were not paid much (if at all at the time) and they most certainly did not (always) care too much about reputation or honor. Soldiers got their main source of income and joy by plundering people and places. The spoils of war if you would. Now, there is a term for it, called the "Tax of Violence".^[1] This basically meant that the soldiers would take things that they wanted from surrounding areas where the army camped and marched, and from whomever they so desired. It did not matter which side the peasants/populace were on or loyal to. When would these peasants attack them? Well, the peasants would not just attack the soldiers when they were at camp, they would ambush them to seek revenge. Sometimes they would ambush small parties on the road, or if they found sleeping soldiers, they could attack them as well.
There are several examples in painting of these (although these are just representations, as far as I know) events happening. This one shows some peasants and soldiers outside of a tavern. The weapon the guys is using? A flail.
This page gives you some good examples of what the soldiers did. The first one shows them pillaging a farmhouse. These are events which caused the peasants to do things like this and this. All of these are actions in which farmers and peasants took up what arms they could, especially farming flails, to attack and kill soldiers.
In all of those pictures linked, some peasants are using a flail. I know that they are not all just soldiers in an epic battle, wearing armor and the like, however, these were times of war. I have not seen that many times in movies or television where this was shown. Mostly, you see the poor peasant trying to defend his home or farm as soldiers ride by and kill him.
I could not find all of the pictures I wanted sadly, although I hope that this is sufficient enough to give you and idea of how a farming flail was, to good effect, used outside of the army. I do hope that a flaired user or someone with more sources readily available would be able to step in as well.
In the time period the flail was used (1300s-1500s) it wasn't very prevalent for two main reasons. Firstly, the flail wasn't considered an honorable weapon. During that period of time, there was a code of chivalry that dictated how knights should battle. Generally battles between knights weren't to the death, but rather to see which knight could best their opponent. Because the flail was designed to pierce armor and kill, it wasn't considered chivalrous. Secondly, the flail just wasn't a very good weapon when considering the other choices a knight had, with a wide variety of swords for all types of fighting, or battleaxes.
Sources:
http://www.lordsandladies.org/flail.htm
http://www.lordsandladies.org/middle-ages-weapons.htm
