WHAT separates the good from the great? Charnwood Dynamics, a British firm, hopes to find out—at least in the realm of football. Though the beautiful game, as its fans refer to it, requires many skills, one useful one is to be able to score goals from free kicks. A free kick, for non-soccer-enthusiasts, is a free shot awarded to one side in the wake of a serious infringement of the rules by the other. For some sorts of free kick, if he is within range of the goalmouth, the kicker can attempt to score from it, but the opposing team will usually try to stop this by lining their men up in a defensive wall between the kicker and goal. If the kicker is able to apply topspin to the ball, however, he can send it over the wall on a curving path that then carries it downwards below the goal’s crossbar, in order to score. Today, the leading practitioners of the art of topspin are Juninho Pernambucano and Marcos Assunção of Brazil. But players and coaches everywhere would love to be able to turn that art into science by capturing exactly what is going on and mimicking it. With the aid of Charnwood’s technology, they may be able to do so. The technology in question is a motion-capture system. Such things are, in themselves, nothing new. They are used, for example, to make animations in which the action of a cartoon character is based on the movement of a real actor. But, since sport is all about controlled movement, they should be an ideal way of working out what makes a good sportsman—except that motion-capture technology does not work well out of doors. Motion capture relies on putting markers on crucial parts of a person’s body—his hands, feet, elbows and knees, for example—and using a camera to follow those markers’ movements. Sometimes the markers emit light. Sometimes they reflect beams broadcast from spot lamps. Either method is suitable for use in a studio, but outdoors, where the intensity of the ambient light is much higher, the cameras tracking the markers struggle to distinguish signal from background.

Charnwood reckons it has solved that problem with a device called CodaSport. This uses specially bright light-emitting diodes on the markers (though the flashes these make cannot be seen by the naked eye, as they are in the infra-red part of the spectrum). Although they are bright, however, the flashes are also short, so as not to drain the battery in the marker too fast. Each lasts a mere ten millionths of a second. And, crucially, the diodes flash in sequence, so that the detector knows which marker is which, simply from the time of the flash.

To process these transient flashes, Charnwood has souped up its cameras. Each has three sensors, and each sensor is composed of a row of 32 individual light detectors. Unlike the detectors in a normal camera, each of those in CodaSport has it own amplifier. That enables the system to react quickly, and thus deal with very short flashes. Also, the middle sensor is at right angles to the other two, which lets the system triangulate the distance to each marker within a fraction of a millimetre.

In front of every sensor is a filter that has a pattern of black lines on it. These lines cast shadows on the detectors, and the movement of the shadows can be converted, by suitable algorithms, into the movement of the markers and thus of the player himself. The result is then turned into an animated model on a computer screen, so that interested parties can see what is going on.

Ashley Gray, a sports scientist at Loughborough University, in England, is one such party. In June he set up an experiment that uses CodaSport to study how players take free kicks. His experiment involved four experienced footballers, two of whom had received training from Bartek Sylwestrzak, a specialist kicking coach, in how to put apply top spin to a free kick, and two of whom had not.

Each participant wore 28 markers attached to his boots and legs. He was then asked to kick a ball repeatedly over a barrier representing a wall of opposing players and into a goal, at speeds that could beat a goalkeeper.

Dr Gray is currently sifting through the data, in order to work out the crucial elements involved in putting topspin on a football—particularly the horizontal angle of the striking foot in relation to the ball, and its vertical angle relative to the ground. That done, he will add extra markers to the players’ bodies to study the position, velocity and acceleration of other parts of the anatomy, in order to see how these contribute. The result, he hopes, will allow the application of topspin to be taught more accurately. Free kicks will then become more valuable. The goalkeeper’s job will become a bit harder. And perhaps the game will become somewhat cleaner, as those who might infringe the rules think twice about the consequences of their actions.