In cricket, a googly is a type of delivery bowled by a right-arm leg spin bowler. It is occasionally referred to as a Bosie (or Bosey) after its inventor Bernard Bosanquet; in Australia it is commonly referred to as a wrong'un (and in India as the wrong one, which led to the naming of the doosra, meaning the other one, named by its inventor Saqlain Mushtaq).
While a normal leg break spins from the leg to the off side, away from a right-handed batsman, a googly spins the other way, from off to leg, into a right-handed batsman (and is distinct from an off break delivery). The bowler achieves this change of spin by bending the wrist sharply from the normal leg break delivery position. When the ball rolls out of the hand (from the side near the little finger, as in a normal leg break), it emerges with clockwise spin (from the bowler's point of view). A googly may also be achieved by bowling the ball as a conventional leg break, but spinning the ball further with the fingers just before it is released.
The change of wrist action can be seen by a skilled batsman and the change of spin allowed for when playing a shot at the ball. Less skilled batsmen, or ones who have lost their concentration, can be deceived completely, expecting the ball to move one direction off the pitch, only for it to move the other direction. If the batsman is expecting a leg break, he will play outside the line of the ball after it spins. This means the ball can either strike the pads for a potential LBW appeal, or may fly between the bat and the pads and hit the wicket.
The googly is a major weapon in the arsenal of a leg spin bowler, and can be one of the bowler's most effective wicket-taking balls. It is used infrequently, because its effectiveness comes mostly from its surprise value.
Left-arm unorthodox spinners, commonly known as "chinaman" bowlers, can bowl with the googly action using the left arm. This delivery is usually known as a chinaman googly and turns away from a right-handed batsman, like a leg break or left-arm orthodox spinner. The googly is similar in principle to the doosra, the ball from an off-spinner which turns the opposite way from his stock ball.