as a sword and boarder, there is nothing more enraging then getting team horse bumped from behind.
If im fighting someone im focusing on them, if i hear a horse coming I assume its an enemy, if you don't assume its an enemy your going to die. So yes, if a friendly bumps me and i Die instantly because im laying on the ground getting stabbed, IT IS YOUR FAULT.
I get killed almost as much to friendly cav(friendly bumps = knockdown = death) as i do to enemy cav.