How many people do you have on screen at one time? I have find doing this somewhat impossible because I have the battlesizer mod making it literally 100 dudes at a time vs my 20. In this incident no matter how good my troops are they are simply over swarmed and ripped down from there horses in a moshpit mess. Or is your dude just a super beast that can solo armies?
I gues this has something to do with the skill tactics which improves your battle advantage