In cricket, a no-ball is an illegal delivery to a batsman. It is also the Extra run awarded to the batting team as a consequence. For most cricket games, especially amateur ones, the definition of all forms of no-ball is from the MCC Laws of Cricket
The delivery of a no-ball results in one run - two under some regulations - to be added to the batting team's score, and an additional ball must be bowled. In addition, the number of ways in which the batsman can be given out is reduced to three. In shorter competition cricket, a batsman receives a free hit on the ball after any kind of no-ball (see below). This means the batsman can freely hit one ball with no danger of being out in most ways.
It is also a no-ball when the bowler's back foot lands touching or wide of the return crease.
A delivery may be judged to be a no-ball by the umpire because it is dangerous or unfair, i.e. a fast short pitched delivery (a "bouncer") may be so judged, and any high full-pitched delivery (a "beamer"), or any deliberate front-foot fault (deliberate overstepping), is inherently dangerous or unfair.
Any beamer is unfair and therefore a no-ball, but the Umpire may judge that a particular beamer is not also dangerous, and does not warrant a warning or suspension 
For deliberate beamers and deliberate overstepping, the bowler may be suspended from bowling immediately, and the incident reported. For other dangerous and unfair no-balls, or for throwing, repetition will have additional consequences for the bowler and team. The bowler may be suspended from bowling in the game, reported, and required to undertake remedial work on his bowling action.
A no-ball may be called for several reasons, most commonly because the bowler breaks the first rule below (a front foot no-ball), and also frequently as a result or dangerous or unfair bowling.
The umpire will call a no-ball in any of the following situations:
In professional cricket, the Laws of Cricket are often modified by a playing regulation that any ball over head height is a Wide ball, but a second fast ball above shoulder height in an over is a no-ball, e.g. in International T20 Cricket and IPLT20. But in International One-Day Cricket and in Test Cricket, two fast pitched short balls per over may pass over shoulder height before no-ball is called, and again any ball over head height is a Wide. Thus competition rules may both tone down the definition of 'dangerous and unfair' (a Wide is a lesser sanction than a no-ball, and cannot be applied if the batsman hits, or is hit by, the delivery) and put definite limits on repetition, intended not only to protect the batsman but also to maintain a fair contest between bat and ball, preventing such bowling being used to limit the batsman's ability to score. There is presently some difference of opinion between the authorities that is evident in the differences between Law and regulation.
By default, it is the bowler's end umpire who calls and signals no-ball. When judgement of ball height is required (for beamers and short balls), his colleague (the striker's end umpire) will assist him with a signal.
In the event of a wicket, the umpire can signal a no-ball after the fall of that illegal wicket and call back the batsman. Either umpire may call a bowler for throwing, although the striker's end umpire is naturally better-placed, and so has the primary responsibility.
The striker's end umpire calls no-ball for infringement by the wicket-keeper, and for position of the fielders, but the bowler's end umpire calls no-ball for fielder encroachment on the wicket.
The bowler's end umpire initially signals a foot-fault no-ball by holding one arm out horizontally and calling "no-ball", which may give the batsman some warning that the ball is an illegal delivery. Other reasons for a no-ball, e.g. illegal position of fielder, throwing the ball, or height of delivery, are initially judged by the square leg umpire, who indicates his judgement to the bowler's end umpire.
When the ball is dead, the umpire will repeat the no-ball hand signal for the benefit of the scorers, and wait for their acknowledgement.
A batsman may not be given out bowled, leg before wicket, caught, stumped or hit wicket off a no-ball. A batsman may be given out run out, hit the ball twice, or obstructing the field. Thus the call of no-ball protects the batsman against losing his wicket in ways that are attributed to the bowler, but not in ways that are attributed to the batsman's running or conduct.
When a no-ball is bowled, runs are awarded to the batting team. In Test cricket and One Day International cricket the award is one run; in some domestic competitions, particularly one-day cricket competitions, the award is two runs. All such runs are scored as extras and are added to the batting team's total, but are not credited to the batsman. For scoring, no-balls are considered to be the fault of the bowler (even if the infringement was committed by a fielder), and are recorded against the bowler's record in their bowling analysis.
In addition, if the batsman hits the ball he may also take runs as normal, which are credited to him. If he does not hit it, byes or leg byes may be scored. Depending on the reason for the umpire's call of 'no-ball' (and hence its timing), the speed of the call, the speed of the delivery and the batsman's reactions, the batsman may be able to play a more aggressive shot at the delivery, safe in the knowledge that he cannot be dismissed by most methods.
If this competition mandates a free hit for the type of no-ball he has adjudged, the umpire will then signal that the next ball is a free hit by making circular movements in the air by extending one raised hand.
The fielders are required to stay in the same positions, and the batsman is again protected from most forms of dismissal under the no-ball Law. The free hit may also be ruled a no-ball or Wide, in which case the next ball is also a free hit, and so on. Once the bowler has bowled one legitimate 'free hit' ball, one ball is deemed to have been bowled towards the (usually six) legal balls required for one over, which then continues as normal. If the batsmen run an odd number of runs on the no-ball, the other batsman is now the striker, and the field may be re-positioned for the free hit. In fact re-positioning is also allowed if the striker changes for whatever reason, for example if a new batsman replaces a striker who is run out on the no-ball, short of making his ground on a second run. The field must also be re-positioned if the no-ball was called for an illegal field placement.
If a ball qualifies as a no-ball and a wide, it is a no-ball.
As stated above, the effects of no-balls may be cumulative, and may reach beyond the completion of the game. Law 41 deals with dangerous and unfair play, and no-balls, in common with most transgressions of Law 41, may cause the umpires to initiate further sanctions. The bowler may be prevented from bowling for the rest of the innings, may face disciplinary action by bodies governing the game, and may be required to change the way he bowls. This is also the case for a bowler called under Law 21 for throwing. Sanctions now also apply for the deliberate bowling of front foot no-balls. Law 41 gives the umpires specific duties to ensure the safe conduct of the game in the case of unfair bowling.
Special complications arise in the professional game when technology is used to assist the umpires, and overturn a decision made on the field. Video review by the third umpire may reveal that a no-ball should have been called (especially for overstepping or a beamer) when the batsman has been given out. If so, the ball is deemed to be dead from the moment of the 'dismissal event,' and any runs scored after that point (runs, byes or leg byes) will not count, but the batting team do get the no-ball penalty. It is now customary for a batsman given out to stand at the edge of the playing area and wait to see if the video may discover a no-ball, in which case he is reinstated. If the batsmen have crossed in running, the batsmen do not return to their original ends. Video review may also reveal that a no-ball should NOT have been called, in which case the ball becomes dead at the time of the on-field call.
Further consequences can occur in cases when the on-field decision has been overturned. For example, the batsman is given out LBW, but the ball runs away off his pads, for what would be 4 leg-byes that win the game. The bowling side is thought to have won. The review adjudges the bowler to have overstepped. The batting team are awarded only a 1 run penalty for the no-ball, and an extra ball or free hit, but fail to score off it, and the bowling side still win, even though the batting side would have won if the umpire's decision had matched the video evidence discovered, although perhaps the fielding side might have tried harder to save the 4 leg byes had they known the match depended on it.[original research?] For such complications and other reasons, including concern to control the amount of time used in review, the ICC is experimenting with 'no-ball instant notification,' under which the umpire is immediately given the additional information to call no-ball while the ball is still live.
If a 'Player Review' requested by the fielding side upholds a decision of 'Not Out', but a no-ball is discovered by the review, that review does not count as unsuccessful, and does not expend the reviews allocated to them.
Unlike some breaches of Law 41, a no-ball only attracts the no-ball penalty (e.g. one run), there are no provisions in the Law or in common regulations for five penalty runs to be awarded to the batting team, and there are no incidents when five penalty runs are awarded that would require a no-ball to be called, although scenarios exist in which five penalty runs might be awarded when the ball is in play and would count in the over, were it not a no-ball for the reasons given here, for example: repeated damage to the wicket by the fielding team during a no-ball, or the ball hits a helmet on the ground during a no-ball.
Throughout cricket history, there have been occasions when the fielding team has needed to encourage the batting team to score freely and quickly, usually when enticing them not to settle for a draw, but sometimes to satisfy some competition rule. In some such cases, especially when the end of the match requires the completion of a specified number of overs, the fielding captain has encouraged his bowler to bowl deliberate no-balls by overstepping. Sometimes it has proved to be an ill-judged idea that risked both bringing the game into disrepute and losing the match, e.g. From Oct 2017, this specific resort is no longer available, as a side-effect of the fact that deliberate overstepping will immediately be ruled "dangerous and unfair" by the umpire, but no-balls that breach other parts of the Law might still be concocted deliberately without being ruled unfair.
The 1774 Laws of Cricket state "The bowler must deliver the Ball with one foot behind the Crease even with the wicket ... If he delivers the Ball with his hinder foot over the Bowling crease the Umpire shall call no Ball (sic), though she be struck or the player is Bowled out; which he shall do without being asked, and no Person shall have any right to ask him."
In the 1788 MCC code this became "The Bowler Shall deliver the Ball with one foot behind the Bowling Crease, and within the Return Crease...if the Bowler's foot is not behind the Bowling Crease, and within the return Crease, when he delivers the Ball, [the Umpires] must, unasked, call No Ball."
The early Laws do not define any consequence of No Ball. It is implied that, when called No Ball, the ball was not in play,  probably regarded as 'dead,' and the batting team did not benefit. No 'notch' was scored.
At some point before 1811, the batsman was allowed to score runs from the no-ball, and was protected from being out, except by being run out. By this change the no-ball became a passage of play, and was probably intended to restrain the development of roundarm bowling. Further complicated modifications were made before 1817, then simplifications between 1825 and 1828 that expressly forbade roundarm. 
In 1829 the one run penalty was introduced for a no-ball when no run was scored otherwise.
The 1835 code legitimised roundarm bowling, and prevented overarm bowling by penalty of no-ball (see also 1835 English cricket season). The previous Laws did not disbar either, but had been interpreted variously by umpires reflecting custom and practice, at some cost to the careers of the bowling innovators. Further changes were made in 1845, and in 1864 bowlers were finally free to bowl overarm, enshrined in the pithy phrase "The ball must be bowled."
In 1835 The Umpire was required to call no-ball immediately the ball was delivered.
Under the 1884 code, a no-ball was called under Law 10 "The ball must be bowled; if thrown or jerked the umpire shall call No ball." and Law 11 "The bowler shall deliver the ball with one foot on the ground behind the bowling crease, and within the return crease, otherwise the umpire shall call No ball." Law 16 provided that "if no run be made one run shall be added to that score." Other detail was codified by Laws 13 (not to count in over), 16 (scoring runs and protection from being out), 17 (scoring of extras), 35 (failed attempt at run out before delivery), 48A (umpire call of no-ball) and 48B (umpire to make call immediately) 
A 1912 revision ruled that the batsman could not be stumped from a no-ball. This caused difficulty until 1947 when he distinction between 'run out' and 'stumped' was clarified.
The 1947 code removed the requirement for the bowler's back foot to be on the ground behind the bowling crease at the moment of delivery. The change codified general umpiring practice, as the judgement had proved difficult to make.
Until 1963, a no-ball was called when the bowler's back foot landed over the bowling crease (which is why the bowling crease was so called), exactly as in 1774. But it was felt that the tallest fast bowlers, able to bowl legally with their front foot well over the popping crease, were gaining too great an advantage. Bowlers also became skilled in dragging their back foot. The change in the Law led to an increase in no-balls: in the 1962-63 series between Australia and England there were 5 no-balls; in the series between the two teams three years later there were 25.
Until 1957, there was no limitation on fielders behind square on the leg side. The change is often attributed to the desire to thwart bodyline, but the Bodyline Controversy was in 1933. The conservative instincts of cricket, and the intervention of World War II, may have been factors in the delay, but as the bodyline article explains, there was more than one reason for the change. Initially a no-ball under "Experimental Note 3 to Law 44" was confined to first class cricket (including all international cricket) and became part of the Laws of Cricket as Law 41.2 in 1980.
In 1980, the main codification of no-ball Law became Law 24, with no-balls also called under Law 40 (the wicket-keeper), Law 41 (the fielder) and Law 42 (Unfair Play). The new code made encroachment onto the wicket by the wicket-keeper and fielders a no-ball. In old film footage, for example of Underwood's Test in 1968, close fielders can be seen in positions that would nowadays cause a no-ball to be called . Previously the fielder could stand anywhere as long as he was still, did not distract the batsman, nor interfere with his right to play the ball. Umpires would conventionally intervene if a player's shadow fell on the pitch, which is still widely treated as a distraction, but not inherently a no-ball.
Prior to 1980, if the wicket keeper took the ball in front of the stumps the umpire would turn down any appeal for a stumping, but would not have called no-ball.
The 1947 code explicitly provided, in Law 26 Note 4, that it was not a no-ball if the bowler broke the bowler's end wicket. No such explicit words appear in the 1980 code.
From 30 April 2013 (ICC playing regulation) and 1 Oct 2013 (Law) a no-ball results when the bowler breaks the non-striker's wicket during the act of delivery. For a short period prior to this, umpires had adopted the convention of calling 'dead ball' when this happened. See Steven Finn for origins of the change.
The year 2000 Code was a major change, and added the no-ball sanction for waist-high fast beamers, balls bouncing over head height, and balls bouncing more than twice or coming to rest in front of the striker. It also removed the judgement of intent to intimidate on fast short pitched bowling.
Since the mid 1980s, no-balls have been accounted against the bowler in calculating his statistics 
Prior to 2000, one no-ball run penalty was only scored if no runs were scored otherwise.
The change to a maximum of one single bounce became Law in all forms of cricket in the Oct 2017 Law code, which also outlawed a ball that bounced off the pitch even if it then became playable.
Between 2000 and 2017, a beamer was judged a no-ball under the Laws of Cricket if it passed the batsman above waist height, when delivered by a fast bowler, or above the shoulder when delivered by a slow bowler. The professional regulations did not tolerate the slow shoulder-high beamer. The Oct 2017 changes set the limit for beamers in all cricket at waist height, regardless of delivery speed.
The Oct 2017 Law code changes also removed the need for repetition before calling a no-ball for dangerous short-pitched bowling (bouncers), introduced the judgement of repetition in head-high bouncers as unfair, and treated a deliberate front foot no-ball as 'dangerous or unfair,' with immediate sanctions as for a deliberate beamer. The new code reduced the warning for throwing to one first and final, instead of the two warnings that had existed since 2000. An explicit penalty for underarm bowling was stipulated, although such bowling was deemed a no-ball in 2000. Interception of the ball by a fielder before reaching the batsman became an explicit no-ball.
Laws were also renumbered so that no-balls are now called under Law 21 (was 24), with no-balls also called under Law 27 - the Wicket-Keeper (was 40), Law 28 - the Fielder (was 41) and Law 41 - Unfair Play (was 42).
Prior to 2017 any byes and leg byes taken from a no-ball were scored as no-ball extras, but are now scored as bye and leg bye extras.
From April 2019 any beamer is unfair and therefore a no-ball, but the Umpire can now judge that a particular beamer is not also dangerous, and does not warrant a warning or suspension. The 2019 code defines what 'waist' means for the first time .
The conventional notation for a no-ball is a circle. If the batsman hits the ball and takes runs, a boundary 4 or boundary 6 off the delivery, then the runs are marked inside the circle. In practice it is easier to write down the number then encircle it.
If the batsmen run byes following a no-ball, or the ball runs to the boundary for 4 byes, each bye taken is marked with a dot inside the circle. Again it is easier to encircle the dots.