Cav charge has the ability to punch a hole thru a line of spear be it yari ashigaru in spear wall or the more reliable yari samurai. Veteran cav is even more capable of doing this with their crazy charge value. Best way to intercept this charges is with your own cav followed up by spears or to put the spear in the way and support with your cav, either way works. But you still have to move those precious archers/matchlocks away from the action asap as soon as you see them coming.