What Is a Legal Bowling Action? Chucking, the 15-Degree Rule, and ICC Biomechanics
The Laws and ICC regulations governing what constitutes a legal bowling delivery — why 'throwing' (chucking) is prohibited while bowling is permitted, the 15-degree elbow flexion rule introduced in 2000 that replaced subjective umpire judgement, how biomechanical testing works, the high-profile chucking controversies (Muttiah Muralitharan, Shoaib Akhtar), and why the rule was impossible to enforce purely by eye.
The Distinction Between Bowling and Throwing
Law 21 prohibits a bowler from 'throwing' the ball — delivering it with a 'jerk' of the elbow rather than a smooth bowling arm motion. The historical principle: a legitimate bowling action involves the arm swinging from the shoulder and the elbow remaining in a fixed flexion state through the delivery — the arm pivots at the shoulder, not the elbow. A throw uses elbow extension at the point of delivery to add additional force, in the same way an outfielder throws to the keeper. The problem: the distinction between 'bowling with arm swing' and 'throwing with elbow extension' was entirely subjective when evaluated by umpires watching at real speed — a bowler with an unusual action that produced borderline elbow extension was impossible to judge fairly without scientific measurement.
The 15-Degree Rule
In 2000, the ICC introduced an objective biomechanical standard: a bowling action is legal if the elbow extension (the straightening of the elbow from its initial flexed position to the final release position) does not exceed 15 degrees during the delivery stride. An elbow extension of 0-15 degrees is acceptable; beyond 15 degrees is considered a throw. The 15-degree threshold was established based on biomechanical research showing that virtually all bowlers — including those with completely clean actions — show some natural elbow straightening through the delivery stride, and that 15 degrees represented a threshold below which the additional velocity benefit of elbow extension was negligible. The rule also acknowledged that many bowlers have elbow hyperextension (the arm appears more bent than it actually is due to skeletal structure) that could be mistaken for throwing visually.
Reporting and Biomechanical Testing
When an on-field umpire suspects a bowler's action, they report it to the match referee after the match. The bowler is then referred for biomechanical testing at an ICC-approved laboratory (typically using high-speed 3D motion capture). The test measures elbow extension across multiple deliveries of all types (pace, variations). If the test confirms extension beyond 15 degrees on specific delivery types, the bowler must remodel their action before returning to international cricket (or is suspended from bowling that specific delivery type). A re-test is required to confirm the remodelled action is compliant. The process aims to be a corrective pathway rather than a punishment — bowlers are encouraged to remodel and return.
Frequently asked questions
Can a bowler switch from a legal to an illegal action mid-career?
Yes — a bowler's action can be reported and found illegal at any point in their career, not just at the start. A bowler who has played for years without suspicion can develop elbow extension beyond 15 degrees as their technique evolves or as they add a new variation. The reporting system operates in both directions: experienced international players have been reported and tested mid-career (Saeed Ajmal, Pakistan spinner, had his doosra found illegal and remodelled it in 2014 despite being highly experienced at international level). There is no protected status based on years of play — the biomechanical standard applies continuously.
Does a higher elbow extension automatically produce more speed?
Yes — elbow extension at delivery (straightening the elbow during the throw) is the biomechanical mechanism by which throwers add velocity beyond what pure shoulder rotation provides. This is why throwing a cricket ball by a fielder produces higher speeds than bowling it in a legitimate action — the fielder can freely extend their elbow through the throw. Bowlers who genuinely throw (excessive elbow extension) therefore gain a velocity advantage over legitimate bowlers at the same physical size and strength. This unfairness to legitimate bowlers — not primarily the difficulty for batsmen — is the reason throwing is prohibited.
How is a 'suspect action' reported by umpires during a match?
Under ICC playing conditions, an on-field umpire who suspects a throwing action can report it to the match referee after the match — they do not call a no-ball or interrupt the game for a suspect action (unless the throw is so extreme it constitutes an obvious jerk visible in real time, which is essentially never the case at international level). The umpire files a confidential report identifying the bowler and any specific deliveries of concern. The match referee notifies the player's national board and the ICC, which then arranges biomechanical testing within a specified timeframe. The bowler can continue playing internationally until the test result is known, unless the board voluntarily withdraws them during the process.