Laws of Cricket 1947 Code - Law 26
For a delivery to be fair the ball must be bowled, not thrown or jerked; if either Umpire be not entirely satisfied of the absolute fairness of a delivery in this respect, he shall call and signal "Not Ball" instantly upon delivery. The Umpire at the Bowler's wicket shall call and signal "No Ball" if he is not satisfied that at the instant of delivery the Bowler had at least some part of one foot behind the Bowling crease and within the Return crease, and not touching or grounded over either crease.
Notes on Law 26
1. Subject to the provisions of the Law being complied with, a bowler is not debarred from delivering the ball with both feet behind the bowling crease.
2. The striker is entitled to know whether the bowler intends to bowl over or round the wicket, overarm or underarm, right or left handed. An umpire may regard any failure to notify a change in the mode of delivery as "unfair", if so, he should call "No Ball".
3. It is a "No Ball" if the bowler before delivering a ball, throws it at the striker's wicket even in an attempt to run him out (see Law 46 Note 4 (vii)).
4. If a bowler break the near wicket with any part of his person during the delivery, such act in itself does not constitute a "No Ball".
5. The umpire signals "No Ball" by extending one arm horizontally.
6. An umpire should revoke the call "No Ball" if the ball does not leave the bowler's hand for any reason.
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