The main aim of spin bowling is to bowl the cricket ball with rapid rotation so that when it bounces on the pitch it will deviate from its normal straight path, thus making it difficult for the batsman to hit the ball cleanly. The speed the ball travels is not critical, and is significantly slower than that for fast bowling. A typical spin delivery has a speed in the range 70–90 km/h (45–55 mph). However, in 2010 Shahid Afridi of Pakistan bowled the fastest spin delivery of 134 km/h in a T20 match against New Zealand
Spin bowling is divided into four different categories, depending on the particular physical technique used. There is virtually no overlap between the two basic biomechanical techniques of wrist spin and finger spin.
Depending on technique, a spin bowler uses either predominant wrist or finger motion to impart spin to the ball around a horizontal axis that is at an oblique angle to the length of the pitch. This sort of spin means it is also possible for the Magnus effect to cause the ball to deviate sideways through the air, before it bounces. Such deviation is called drift. The combination of drift and spin can make the ball's trajectory complex, with a change of direction at the bounce.
This variety of trajectories achievable by a spin bowler can bewilder inexperienced or poor batsmen.
Spin bowlers are generally given the task of bowling with an old, worn cricket ball. A new cricket ball better suits the techniques of fast bowling than spin bowling, while a worn one grips the pitch better and achieves greater spin. Spin bowlers are also more effective later in a game, as the pitch dries up and begins to crack and crumble. This again provides more purchase for the spinning ball and produces greater deviation. Spin bowlers that open the bowling are rare, but became a more a viable option with the introduction of Twenty20 cricket when pitch conditions are in their favour, and the ball also generally drifts more in the air.