Eldorell
Recruit
One option is to have the majority of the casualties you take be injuries, so that you can keep the troops if you win the battle but you don't get to fight the siege with them.
A better option would be to have a fight to get in. This could be made easier if the castle has a hidden entrance meaning you don't need to go through the main gate. I really like this option as it brings an alternative tactical situation. You are not trying to kill everyone, just enough of them to break through the lines. Waiting until night time seems sensible.
I'd also like this expanded so you could do this to try to deliver supplies to a starving garrison.
A better option would be to have a fight to get in. This could be made easier if the castle has a hidden entrance meaning you don't need to go through the main gate. I really like this option as it brings an alternative tactical situation. You are not trying to kill everyone, just enough of them to break through the lines. Waiting until night time seems sensible.
I'd also like this expanded so you could do this to try to deliver supplies to a starving garrison.