I've got some tactics for it.
It's usual that I'll have a bunch of light spearmen, and are facing an army of mailed knights and enemy spearmen.

What I do is place a schiltron in front of my line, and place the other units behind. The Schiltron has a better defense against the cavalry, so when the mailed knights charge in, they get stuck against the schiltron. If they charge you, they take on the schiltron first, breaking apart that massive wave of horseflesh and manpower. You then throw your infantry in against the enemy spearmen and cavalry, who are hacking apart your infantry. You'll lose alot of one unit this way, so I suggest mercenary spearmen.