It probably is I suspect as it was the Duke of Wellington following the Battle of Waterloo that is supposed to have said the Battle was won on the playing fields of Eton
Henry V was born in Monmouth (Wales ). His star archers, who won him the battle, were born in Wales. So it was won, if like Waterloo 400 years later, on some playing fields, those were playing fields of Wales, somewhere (Strady Park perhaps?)