Jumper classes are held over a course of show jumping obstacles, including verticals, spreads, double and triple combinations, usually with many turns and changes of direction. The intent is to jump cleanly over a set course within an allotted time. Time faults are assessed for exceeding the time allowance. Jumping faults are incurred for knockdowns and blatant disobedience, such as refusals (when the horse stops before a fence or "runs out") and it affects the time required to complete the course. Horses are allowed a limited number of refusals before being disqualified. A refusal may lead to a rider exceeding the time allowed on course. In most competitions, riders are allowed to walk the initial course, but not the jump-off course (usually the same course with missing jumps, e.g., 1, 3, 5, 7, 8 instead of 1, 2, 3, 4, 5, 6, 7, 8, 9) before competition to plan their ride. Walking the course before the event is a chance for the rider to walk the lines he or she will have to ride, in order to decide how many strides the horse will need to take between each jump and from which angle. The more higher levels of competition, such as "A" rated shows in the United States, or the international "Grand Prix" circuit, present more technical and complex courses. Not only is the height and width ("spread") of an obstacle increased to present a greater challenge, technical difficulty also increases with tighter turns and shorter or unusual distances between fences. Horses sometimes also have to jump fences from an angle rather than straight on. Unlike show hunter classes, which reward calmness and style, jumper classes require boldness, scope, power, accuracy, and control; speed also is a factor, especially in jump-off courses and speed classes (when time counts even in the first round). A jumper must jump big, bravely, and fast, but also must be careful and accurate to avoid knockdowns and must be balanced and rideable in order to rate and turn accurately. In a jump-off, a rider must balance the need to go as fast as possible and turn as tightly as possible against the horse's ability to jump cleanly with good scope.
Equestrian Summer London Olympics 2012 are scheduled to be held between 28 July and 9 August, at the Greenwich Park venue in London.