[My original cavalry charge posts from 2006 have been deleted because they were obsolete. The new versions from 2012 can be found under the cavalry charges tag.]
Empirical evidence of horse collisions is very difficult to get. The best I could do back then was the footage of Anmer hitting Emily Davison in the 1913 Derby.
Now Peter at That’s Pretty Lame has found exactly what I needed: YouTube footage of two horses colliding head-on at a full gallop. According to the commentary this happened at Prescott Downs, Arizona on 26 August 2000. Both horses were killed and jockey Stacy Burton suffered severe brain injury. I shouldn’t be pleased about such a tragedy, but it’s the perfect empirical evidence to prove my point.
If only I’d thought of searching YouTube for horse collisions, but I assumed they were so rare that I wouldn’t find one. In fact that isn’t the only one. This is another – it looks like the collision is at a slower speed than the Prescott Downs accident but both horses are brought down. In this one the collision is at a very slow canter – looks like no-one was hurt but the riders only just stayed on. This is about as close as you can get to knocking the enemy out of the way with your momentum, but I think it supports my point that the effects of a collision are equally bad for both parties (just as Isaac Newton predicted – who’d have thought it?). So the bay barged past the grey and kept going, but if this was a cavalry charge I don’t think you could really say that the bay won. Both sides would be disordered and neither would have gained an advantage.