A rather large stone used as a form of primative weaponary. So named as when thrown it requires one to crouch down or as the term goes 'to duck.'
'Ducking' was primarily considered the best form of defence against such attack until, as a species, we became more intelligent and in fact 'running' is now considered much more effective. This may be for two reasons; 1.) Attackers were becoming more wise to such 'ducking' and therefore proceeded to throw the 'ducker at a lower level, causing many injuries to the back of the head and back. 2.) If running is achieved at a credible pace it limits the possibility of secondary or multiple attacks. Whereas with the primary defence, 'ducking' there was almost always potential for secondary or even multiple ensuing attacks, unless with some luck, the attacker runs out of such ammunition. In which case, usually the 'attacker' then becomes 'defendee.'
Thus, my opinion is that the name of this here weaponary be changed in fact to 'a Runner.' Although I admit, it does not have quite the same ring to it, nor would it prevoke the same sense of fear when used as verbal in attack.
E.g. Dave: 'I'm gonna come over there and knock you out.'
Rob (picking up a rather large stone): 'Come on then!'
Marv, friend of Dave: 'Oh shit, he's gunna lob a ducker.'
Dave: 'Fuck it, run!'