The French commander, d'Albret, blocked the road to Calais and in the resultant battle the masses of English longbows proved devastating to the clumsy French knights.  
A final attack mounted by the Counts Marle and Fauquembergues and an earlier attack on the baggage train likely combined to explain the victorious commander's order to execute prisoners.  The victor's flanks were protected by long stakes driven into the ground while the losers attack was so funneled that they couldn't wield their weapons when they reached the enemy line.  The French commander, d'Albret, blocked the road to Calais and in the resultant battle the masses of English longbows proved devastating to the clumsy French knights.  FTP, name this battle of the Hundred Years' War fought in 1415, a resounding victory of Henry V.
A final attack mounted by the Counts Marle and Fauquembergues and an earlier attack on the baggage train likely combined to explain the victorious commander's order to execute prisoners.  
Battle of Agincourt