Final answer:
The colonists faced a shortage of ammunition at the Battle of Bunker Hill and were unable to prevent the British from overrunning their position. They were forced to retreat and abandon Breed's Hill.
Step-by-step explanation:
The shortage that the colonists faced at the Battle of Bunker Hill was ammunition. They started the day short on ammunition and were unable to fire during the third assault by the British. This prevented them from preventing the British from overrunning their position and ultimately led to their retreat. With few swords or bayonets of their own, the Americans were forced to abandon Breed's Hill.