.. there are times when I thoroughly hate these forums .. it just ate my lengthy post ..
Ok, I'll try again:
No, I'm pretty shure you can't train horse to do that. And as it would be suicidal, noone would even try.
That doesn't mean it couldn't happen by accident. Horse and rider may get confused and/or panicked, and just turn into the wrong direction. And most likely end up dead.
It may even happen that a whole "squad" of knights e.g. comes over a hill and runs into some foot soldiers at full speed. There wouldn't be enough room for the knights to stop or evade, and maybe the horses wouldn't realize fast enough what is happening, especially if they are pressed by their riders. But it would result in a bloody mess.
Especially, if the foot soldiers are prepared and realize that their only chance is to hold the line.
That's what 80% of ancient/mediaval combat is about
: holding the formation. As long as the shield wall holds, the pikes/spears are kept straight, not much could happen. As soon as a formation is broken up, it's overrun by the enemy and slaughtered. (This could happen because of failing morale, a danger which is unexpected or comes from an unexpected direction, obstacles or exhaustion)
Example: Hastings
So the charge of heavy knights was directed at either A) disorganized troops or b) other cavallery, which couldn't hold a tight formation as inf does.
The longer couched lance (which wasn't available at Hastings, and for some hundred years afterwards) was a bigger thread to foot soldiers armed with the usual trusting spears. But the real danger came
not from it being an ultimate weapon, but from it's psychological impact. If the very first line of soldiers in the shield wall
believed the knights could charge them succesfully, turned and ran, the shield wall was actually broken and the knights could have their day.
It was only logical to give longer spears to the infantry as well, discard their shields as they had to handle the long poles 2-handed. To give them more offensive punch (you couldn't really trust with something 4-5m long), it developed into the pike etc. With those, the foot soldiers could counter-attack the knights if they pulled away from the hegde of spear points and had to move "alongside".
Often the knights dismounted to fight in the line
on foot, simply because horses where too expensive and tatctical possibilites too small.
Something to read up you can find here
http://www.dicksonc.act.edu.au/Showc...2/stirrup.html