There are enough caltrops to last for one use only. They may be used when an opponent decides to charge. The defender simply throws the caltrops into the path of his attacker and they reduce his charge range by D6 inches. If this means that the attacker cannot reach his target then it is a failed charge.
Lore
Originally used on the battlefield to impede cavalry charges, a caltrop is a small spiked iron ball. In the City of the Damned a pouch of these small items can be enough to deter any attacker who risks serious injury should they try to charge over them.