perform large, fast circles at a near-gallop and smaller, slow circles at a lope. They should be perfectly round, with the rider dictating the pace of the horse. There should be an easily seen change of speed as the rider transitions from the large, fast to the small, slow circles. Most circles incorporate changes of direction that require a flying change of lead. Flying lead change: the horse changes its leading front and hind legs at the lope mid-stride, during the suspension phase of the gait. The horse should not break gait nor change speed. It can be used for as turning and direction. While completing a change at speed can improve one's score, precision is the most important factor in judging: A horse taking more than one stride to complete the change, or a horse that changes early, late, or that changes only the front feet and not the hind feet will be penalized. Rundown: the horse gallops or "runs" along the long side of the arena, at least from the fence or rail. A rundown is a required movement prior to a sliding stop and a rollback to the designated direction (either towards the judge or towards the nearest wall depending on the pattern). Sliding Stop: the horse accelerates to a gallop and then suddenly comes to a complete halt, planting its hind feet in the footing and allowing its hind feet to slide several feet, while continuing to let its front feet "walk" forward. The back should be raised upward and hindquarters come well underneath. A particularly powerful stop may, depending on arena conditions, produce flying dirt and a cloud of dust. The movement should finish in a straight line, and the horse's position should not change. This movement is a crowd favorite, along with spins (see below). Back or Backup: the horse backs up quickly for at least . The horse must back in a perfectly straight line, stop when asked and hesitate a moment before the next movement. It is judged on how quick, smooth and straight the line is. Rollback: the horse immediately, without hesitation, performs a 180-degree turn after halting from a sliding stop, and immediately goes forward again into a lope. The horse must turn on its hindquarters, bringing its hocks well under, and the motion should be continuous with no hesitation. Spins or Turnarounds: beginning from a standstill, the horse spins