The infamous "trot bump" to help teammates/get a bumpshot is hard to dodge but can't cause that much damage.
That's either a high speed bump or a bump from a very heavy horse. In any case, horses at higher speeds are easier to dodge if you don't mess up your timing. And heavy horses, well, they are made for that and have other problems.
First bump was from Kastamonulu's Champion Cata Horse which is heavy horse. However that horse was straying around and since I play without sound I had no idea that horse is behind me. It wasn't even galloping, it was actually moving very slow. Bumped me from behind and took my last 15% of HP. No one controlled that horse and no one called for him, horse did that to me on it's own. Happened two days ago. Whole server laughed at that
Second situation is when I was trying to kill the riders but some archer killed him, his horse went nuts and bumped me with full speed and that's how I lost 10-15% of my HP and died. Horse in question was Champion Arabian. I don't think that cav is skilled enough to know that he can control the horse few seconds after he dies so that's another death to a damn stray horse. Happened yesterday.
On average light horses (loomed) deal 10-20% damage to me when going full speed per bump, heavy horses do the same but they don't need to move fast at all. As I said, I have 57 body armor and 65 HP.
I'm aware that in old cRPG bump damage was even higher then now but many things were a lot different back then (34 pierce stab on Sword of Tears). I liked when horses dealt little to no damage per bump and that lasted for 10 months I think.
Then came cav maneuver and speed nerf (which I've suggested and it made perfect sense because before that nerf most cav had 50-1 and higher scores). To compensate chadz decided to make horses a bit more realistic, therefore he buffed bump damage and couch damage A LOT but nerfed horse stats.
Since then many changes were made, many things nerfed but cav pretty much stayed the same. Either make cavalry more realistic (like I suggested) or nerf horse bump damage to compensate for many inf and ranged nerfs that happened in the mean time. Realistic change make perfect sense, however like every other realistic change it will force people to play even more cautious (even more backstabbing), so that's a double edged sword I'm afraid.
Before all cav come here crying how they were nerfed for 100 times, I'll just remind them while what they are saying is true, it's also true that cavalry wasn't nerfed for 7 or 8 months.