I'll apologize in advance for the relatively trivial (and probably unanswerable) nature of the question .... but I had the pleasure this evening of chatting to a Danish gentleman, late fifties to early sixties, who stated that he was taught that Vikings in England "invented football" after cutting off the head of an English king and playing with it. He thinks the king was called Edmund (or possibly Edward). He thinks it occurred around or before 800AD. I don't know of any English kings called Edward before The Confessor and I don't know if there were any Edmunds either. My initial Google searches haven't produced any real results except that the Vikings may have kicked heads around. Does anyone have any evidence that his tale is maybe true or just a legend or just his history teacher having a laugh?
I don't think the Vikings killed any Anglo-Saxon King of England. There were certainly Edwards and Edmunds: Edward the Elder (899-924) died fighting the Welsh and Mercians, Edmund I (939-946) murdered by a thief, Edward the Martyr (975-978) murdered in unclear circumstances but by fellow Saxons/English people, and Edmund II Ironside (1016) who died after a deal had been made with Cnut.
2 Scottish kings were killed by Vikings: Indulf, king of Scots 954-962, killed fighting Vikings and Constantine I, king of the Picts 862-877, who according to at least one account, was beheaded on Fife Beach by Vikings. Perhaps the legend evolved from here somehow?