Really wasn't so much a french blunder at Crecy, their cavalry tactics had won them an extremely large country, and the british was basically using tactics one age ahead, replace the bows with guns and they were basically using early modern pike and shot tactics not seen elsewhere until the 16th century. Agincourt, I think the french blundered in not sending in their third line in to the british flank,but I think this was actually the english having advanced tactics than french stupidity.