Leads

What are leads? Well, a 'lead' can either be a right-lead or a left-lead. The 'leading' hoof is the one that lands last in the three beat sequence of a horse's canter. In the canter, a horse can either start with its left or right hind leg. If it starts with its left hind leg, it will have a right-lead (its right fore hoof will be the last hoof to hit the ground), and if it starts with its right hind leg, it will have a left-lead (its left fore hoof will be the last hoof to hit the ground).

The sequence in which the hooves hit the ground at a canter (left-lead)
1. Right hind hoof.
2. Left hind hoof and right fore hoof.
3. Left fore hoof.

The sequence in which the hooves hit the ground at a canter (right-lead)
1. Left hind hoof.
2. Right hind hoof and left fore hoof.
3. Right fore hoof.

The first hoof which hits the ground is naturally the leg that started moving first.

In this fine sketch of a cantering Clydesdale, the horse has just landed his left hind hoof and right fore hoof on the ground. Therefore, he is cantering at a left-lead.