Standard field hockey balls are hard spherical balls, made of plastic
(sometimes over a cork core), and are usually white, although they can
be any colour as long as they contrast with the playing surface. The
balls have a circumference of 224–235 mm (8.8–9.3 in) and weigh 156–163 g (5.5–5.7 oz). The ball is often covered with indentations to reduce aquaplaning that can cause an inconsistent ball speed on wet surfaces.