Yes, this would be a great feature and would make spear/shield viable. It's more a support class anyway, most 1v1 against any other dueling class you would still lose, but at least this gives you a chance.
As to the pike comment before, I think this should be only for those using a 1h spear w/ shield. If anything you could give pikes/2h spears a "bracing" attack that would rear horses, and the normal attack would not.