Seam bowling
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Seam bowling is a technique used for bowling in the sport of cricket. Practitioners are known as seam bowlers.
Seam bowling is generally classed as a subtype of fast bowling, although the bowling speeds at which seam can be a factor include medium-pace bowling.
Physics of seam bowling
A cricket ball is not a perfect sphere. The seam joining the pieces of leather is circumferential and the stitching is noticeably raised. If the ball is bowled such that the seam hits the pitch when it bounces, this irregularity can cause the ball to deviate sideways in its path.
In order to achieve this effect, a seam bowler delivers the ball with the seam held upright, with rotation about a horizontal axis. This keeps the seam aligned vertically as it travels towards the batsman, making it likely that the ball will bounce with the seam on the pitch.
The direction and degree of deviation from a straight path are dependent on the small-scale alignment of the seam and any irregularities in the pitch surface. This means that deviation caused by seam is chaotic and unpredictable.
Often the deviation caused by seam is not large enough to cause a batsman significant problems with playing the ball. Occasionally, however, the ball can deviate far enough to hit the edge of the cricket bat instead of the middle, producing a catch for nearby fielders.
Skilled batsmen have good reflexes and are less troubled by seam bowling than less proficient ones.