because it was too big , or perhaps because he was sweating too much , one man 's helmet had slipped , and another man 's shield was dropping forwards , so that a gap between him and his neighbour , and exposing him from chin to belly to a spear thrust or slashing sword ; and another man had taken off his helmet , and was trying to brush the sweat out of his eyes with his forearm while still holding the helmet clumsily in that hand .