A bowler may bend the wrist, but not throw the ball.

What counts as throwing

A cricket delivery is not illegal just because the action looks unusual, round-arm, slingy, or hard to follow at full speed. The Laws focus on the bowling arm during the delivery swing.

Once the bowler's arm has reached shoulder height, the elbow must not be straightened before release. If the arm is bent and then extends in that part of the action, the delivery may be treated as thrown. The rule does not stop the bowler from using the wrist, fingers, shoulder, or body rotation to bowl the ball.

How an umpire reads the action

1. Watch the bowling arm as it reaches shoulder level in the delivery swing.
2. Judge whether the elbow straightens before the ball leaves the hand.
3. Separate elbow straightening from legal wrist flick, finger spin, shoulder rotation, or a naturally unusual arm shape.
4. If the umpire considers the ball thrown, call and signal no-ball.
5. After the ball is dead, follow the warning, suspension, and reporting procedure if the same bowler throws again in the innings.

Either umpire can call no-ball

The striker's-end umpire has the main viewing responsibility for the fairness of the arm, because that position often gives a clearer angle on the bowler's elbow through the delivery swing. But the bowler's-end umpire is not prevented from calling it.

If either umpire believes the ball has been thrown, that umpire calls and signals no-ball. The call is made without needing an appeal from the batting side, because no-ball decisions are umpire calls, not dismissal appeals.

A thrown delivery is a no-ball

A thrown delivery is treated as a no-ball. The batting side receives the no-ball extra, the delivery does not count as one ball of the over, and the ordinary no-ball limits on dismissals apply.

The ball is not automatically dead just because no-ball has been called. Batters can still run, a boundary can still be scored, and the fielding side can still complete a dismissal that is permitted from a no-ball, such as a run out.

What happens after the call

After a thrown delivery has been called and the ball is dead, the bowler receives a first and final warning for that innings. The bowler's-end umpire informs the fielding captain and the batters about the reason for the action.

If the same bowler throws another delivery in that innings, it is again called no-ball. The bowler is then suspended from bowling for the rest of that innings. If the over is not complete, another bowler must finish it, and that replacement cannot have bowled the previous over or part of it and cannot bowl any part of the next over.

Match reports and competition action

The Laws also require the umpires to report the occurrence after the match to the relevant team executive and governing body. What happens next depends on the competition, because leagues and governing bodies set their own disciplinary and assessment procedures.

At international level, the ICC uses a formal illegal bowling action process. Match officials report a suspected action, the player is assessed at an accredited testing centre, and a bowler found to exceed the ICC's permitted elbow-extension limit can be suspended from bowling internationally until the action is corrected and successfully retested.

The 15-degree limit is an assessment rule

In ICC cricket, an illegal bowling action is defined by elbow extension of more than 15 degrees between the arm reaching the horizontal and ball release. This is a testing and regulatory standard used to assess suspected actions with technology.

That does not mean on-field umpires are measuring angles during the run-up. On the field, they use sight and cricket judgment to decide whether a delivery appears to have been thrown. Laboratory assessment is used later when a bowler's action is formally reported under the relevant playing conditions.

What the rule does not ban

• Wrist movement: a bowler may flex or rotate the wrist during the delivery.
• Finger spin: spinning the ball with the fingers is legal if the arm action remains fair.
• Different release styles: pace bowling, orthodox spin, wrist spin, round-arm actions, and unusual natural actions are not illegal by themselves.
• A bent arm held steady: the issue is straightening during the relevant part of the delivery, not simply whether the arm ever looks bent.

Underarm bowling is a separate issue

Throwing is not the only arm-related no-ball rule. Underarm bowling is not allowed unless it has been specially agreed before the match. If a bowler delivers underarm without that agreement, the umpire calls no-ball and uses the same Law 21 procedure that applies to a thrown delivery.

A bowler also has to tell the umpire whether they are bowling right-handed or left-handed and over or round the wicket. Failing to notify a change of mode is unfair and leads to a no-ball, but it is a different breach from throwing.

Misunderstandings to avoid

• "A bent elbow is always illegal" is too simple. The key question is whether the elbow straightens during the relevant part of the delivery.
• "A strange action must be throwing" is wrong. Unusual mechanics can be legal if the ball is bowled rather than thrown.
• "Only the striker's-end umpire can call it" is wrong. That umpire has the main responsibility, but either umpire may call no-ball.
• "The batter has to appeal" is wrong. No-ball for throwing is an umpire decision made without an appeal.
• "The first call immediately bans the bowler" is wrong under the Laws. The first call brings a first and final warning; a further thrown delivery by the same bowler in that innings brings suspension from bowling for that innings.

Source material

• MCC Law 21: No ball
• MCC Law 41: Unfair play
• MCC Laws of Cricket
• ICC Illegal Bowling Actions
• ICC Playing Conditions