The Battle of Maldon in 991AD which was by all accounts a completely typical English cock-up! The vikings invaded and Byrhtnoth was asked to let them onshore, which he did! It's thought he did this to stop the vikings heading further up the coast and attacking defenceless settlements. His trusted lieutenant Godric then fled the battle on Byrhtnoth's horse, Godric's brothers thought Byrhtnoth was retreating and they all ran away, later realising their mistake they made another stand.
Byrhtnoth's men made a doomed stand against the vikings who won the day. Byrhtnoth's men inflicted such damage on the vikings that they had so few men left to ransack the place, they simply went home rather than bother staying to loot!
Byrhtnoth's decapitated body was later found after the battle.
Typical English cock-up in which we lost but still managed to win by simply causing so much trouble for the enemy they had to give up and go home!