Just think of it as not "blocking" but as a "deflecting the blow".
But the animation would probably be harder, just like a chamber, so instead, ou just have this block. As if a club could upblock an overhead flamburger. xD
Deflecting the blow, done by very good swordsmen, enabled to lower the damage done to the blade, thus preventing chips or cut.
Warband's peasants are master at this, since they can effectively block deflect knight's hits with a club. NERF PEASANTS !