What is the origin of the idiom "on one's heels" and when to use it?

The origin of the idiom "on one's heels" is derived from the literal image of a person or competitor closely following another person or competitor. When one person is directly behind another, they are figuratively said to be "on their heels," emphasizing their proximity and the competitive nature of the situation. While the specific historical origin is not documented, it is a figurative expression that has evolved naturally to describe the dynamics of closely contested races and competitions, where competitors are often equally matched and close to achieving victory.