
Many of us were taught to use pressure and release when working with horses. You apply pressure to the horse, they move away from it and you then release/reward them. Half-halt rein aid, the horse slows its pace and the rider releases the rein.
Sometimes riders forget to fully release when the horse moves away from pressure. They ask the horse to halt, the horse stops and the rider gives a little with the rein. But then they continue to hold the rein, even while the horse is at a halt. I see this quite a bit. The rider thinks they’ve released when they give 10% of the rein. But the horse feels that other 90% as continued pressure.