ACtually... considering that hole isn't going to detract too much from sword (or axe) blows because they are slashing weapons, meaning you swing them at your opponent. This means that the blow will be coming at an angle and would only rarely threaten the middle. Piercing weapons... ie. arrows, spears and the later lightswords like rapiers would seriously be a problem. They were light and maneuverable enough to be able to strike at the unexposed area. Blunt weapons, such as maces, flails and warhammers would be the MOST effective since the force of the blow hammered right chain mail type armor. It was VERY uneffective against any type of weapon that relied on raw force rather than a cutting or piercing edge. Amazing what you learn in the SCA huh?