The Bowling Action

The Bowling Action

The bowling action itself has to conform to several restrictions. The bowler's arm must be straight when the ball is bowled (so no "throwing" is allowed). The ball must be bowled overarm, not underarm.
The difference between 'bowling' and 'throwing': When you throw the ball, the elbow is cocked and used to impart energy to the ball by straightening. When a ball is bowled, the elbow joint is held extended throughout. All the energy is imparted by rotation of the arm about the shoulder, and possibly a little by wrist motion. For a right-handed bowler, the action goes roughly as follows:
After the run-up, the right foot is planted on the ground with the instep facing the batsman. The right arm is extended backwards and down at this stage. The left foot comes down on the popping crease as the bowler's momentum carries him forward - he is standing essentially left-side on to the batsman. As the weight transfers to the left foot, the right arm is brought over the shoulder in a vertical arc. The ball is released near the top of the arc, and the follow-through brings the arm down and the right shoulder forward rapidly.
Bouncing the ball on the pitch is not mandatory. It's usually done because the movement of the ball off the pitch makes it much harder to hit. Unbounced deliveries, or full tosses are almost always much easier to hit, and mostly they are bowled accidentally. A full toss above hip height is no ball, and an umpire who suspects that such a ball was deliberate will give the bowler an official warning. A warning is also given if the umpire believes the bowler is bowling at the body of a batsman in a deliberate attempt to injure the batsman. After two warnings a bowler is barred from bowling for the rest of the innings.
If any rule governing the bowling action is violated, a no ball results.
Bowlers are allowed to polish the ball by rubbing it with cloth (usually on their trouser legs) and applying saliva or sweat to it. Any other substance is illegal, as is rubbing the ball on the ground. Usually one side of the ball is polished smooth, while the other wears, so that the bowler can achieve swing (curving the ball through the air). It is also illegal to roughen the ball by any means, including scraping it with the fingernails or lifting the seam. A bowler who illegaly tampers with the ball is immediately suspended from bowling for the rest of that innings.
The bowler may bowl from either side of the wicket, but must inform the umpire and the batsmen if he wishes to change sides. Bowling with the bowling arm closest to the wicket is called over the wicket, and is most common. Bowling with the non-bowling are closest to the wicket is called around the wicket.
The bowler may abort his run-up or not let go of the ball if he loses his footing or timing for any reason. The umpire will signal dead ball and the ball must be bowled again. If a bowler loses his grip on the ball during the delivery action, it is considered to be a live ball only if it is propelled forward of the bowler. If such a ball comes to rest in front of the striker, but any distance to the side, the striker is entitled to walk up to the ball and attempt to hit it with his bat. The fielding team must not touch the ball until the striker either hits it or declines to do so.
A delivery may also be aborted by the striker stepping away from his stumps, if distracted by an insect or dust in the eye, for example.