This comes from Chapter XIII of the Illustrated History of Ireland by Margaret Anne Cusack.
" The mailed armour of the Danes (Danar) seems to have been a source of no little dread to their opponents. But the Irish battle axe well have set even more secure protection and defiance. It was wielded with such skill and force that, frequently, a limb was lopped off with a single low, despite the mail in which it was encased; while the short lances, darts and slinging stones provided a means of decapitating or stunning a fallen enemy"

 This is the battle in which Brian Boru died.

 Now, as far as I know, the first written account of the Battle of Clontarf was put down almost 150 years later.  I really wonder how accurate a retelling it is after all that time.

Not sure the accounts are very accurate, many were written by Brian Borus descendants looking to use it as self affirming propaganda. No doubt slings were used though.

Not sure what he author means by "while the short lances, darts and slinging stones provided a means of decapitating or stunning a fallen enemy".

Many of the irish would have had a large stone held inside the boss of their shield that they threw at short range before engaging, as well as irish darts but who uses a sling to kill a fallen enemy?