After some testing I came across the infamous cavalry charge bug. But in a good way the head on charge is still random but I found a way to force this charge bug to happen.
You have to get your cavalry into wedgeformation, then show your side to the enemy. When he is about to clash into you press double right klick on the enemy and even a light cav and do some severe damage to a Great Guard unit.
For proof watch this video.
First was Great Guard vs Yari Cavalry
Second, Great Guard vs Light Cavalry
Third and Last Great Guard with 21 Attack and 55 Charge vs Yari Cavalry.