Cavalry should instant kill you or take a lot of health if it runs you over while your down on the ground.. Being trampled by a 1,000+ pound (453.59+ Kg for you Europeans) horse can be very deadly.
yes that's realistic, but would kill the game balance of the mod. i think the big problem is that weapons aren't considered "solid" objects in the game. If I'm not moving and my pike is not being thrusted forward, I would still do massive amounts of damage to a horse who ran into it. But in c-rpg, you have to thrust to do damage. I think if weapons were solid objects, then you could maybe try to implement something like more damage from horses running you over (and horses bodies being deadly if they fly at you).
Most of the time, a "realistic" game, would never work for balance. And if it did, like in some FPS games, it would be the middle ages equivalent of of FPS games where people camp in bushes for 15 minutes a round.
Some "realistic elements" are very nice, but in reality this is an action game, not a realism mod.