Mythology and sport are inseparable. The origin and nature of athletic competition ensures that storylines involving heroes and villains, as well as romanticized tales of bygone feats, will continue to be told as long as one human faces off against another.
Although most modern games — with notable exceptions such as Florence's infamous Calcio Storico — have ditched the all-out violence of their historical antecedents, legends and folklore continue to play an important role in their legitimacy and propagation.
Whether or not William Webb Ellis really invented rugby in 1823 by picking up a ball and running with it during a game of football is irrelevant. The story provides a concrete historical narrative tied to a significant and precise moment in time, in much the same way that Nominosukune’s defeat of Taimanokehaya in 23 B.C. does for sumo.