Illegal Bowling Actions: What Throwing Is and How It's Tested
What constitutes an illegal bowling action in cricket — the 15-degree elbow straightening rule, why throwing gives the bowler an unfair advantage, how the ICC's biomechanical testing procedure works, the history of bowling action controversies (Muttiah Muralitharan, Shoaib Akhtar, recent T20 bowlers), what happens to a bowler who is reported, and why the line between a legal action and throwing is sometimes genuinely difficult to determine.
The 15-Degree Rule
The ICC's current definition of a legal bowling action permits the elbow to straighten (extend) by up to 15 degrees during the bowling action — based on research that found all bowlers straighten their elbow to some degree due to natural physiological variation, and that below 15 degrees this straightening is imperceptible to the naked eye. Straightening beyond 15 degrees constitutes throwing — using the arm like a throw rather than a swing. Throwing gives the bowler an unfair advantage because: it allows the arm to accelerate the ball using the elbow as a pivot (generating more pace and deception than a swinging action allows), and it allows the ball to be released from a higher, more controlled point than the arc of a legal swing.
ICC Biomechanical Testing
When a bowler is reported for a suspected illegal action (by umpires, match referees, or opponent captains), the ICC's testing protocol is triggered. The bowler must attend an ICC-approved biomechanical testing centre within a specified period. Testing uses high-speed cameras and reflective markers on the elbow joint to measure the precise degree of elbow straightening during the delivery action. Multiple deliveries are analysed to identify peak straightening. If the average straightening exceeds 15 degrees, the bowler's action is declared illegal and they are suspended from bowling in international cricket until they have developed and re-submitted a modified legal action.
The Challenge of Visual Judgment
The 15-degree threshold is invisible to the naked eye — umpires cannot judge whether a bowler is straightening by 13 degrees or 17 degrees by watching. The threshold was established precisely because testing showed all bowlers straighten somewhat, and a visual threshold that could be judged by the naked eye would either miss genuine throwers (setting the threshold too high) or incorrectly penalise legal actions (setting it too low). This invisibility creates the awkward situation where bowlers are reported based on umpires' general 'impression' that the action looks suspicious, then tested biomechanically to determine whether the impression was correct. Some bowlers with unusual actions (particularly off-spinners with unusual wrist positions) have been reported despite legal actions upon testing.
Frequently asked questions
What happens if a bowler is found to have an illegal action?
A bowler found to have an illegal action (straightening beyond 15 degrees) is immediately suspended from bowling in international cricket. They may continue playing as a batsman or fielder, but cannot bowl until their action has been reassessed and found legal. The bowler must work with their national board's coaching staff to modify their action and resubmit for testing within the specified period (typically several months). If the modified action tests within the 15-degree threshold, the suspension is lifted. Bowlers may be permitted a 'remedial period' to fix their action without full suspension, depending on the severity and whether they have been previously reported.
Has a fast bowler ever been permanently banned for throwing?
Permanent bans for throwing are extremely rare — the ICC process is specifically designed to allow bowlers to modify and remediate their action rather than simply banning them. Most bowlers who fail action testing are given remedial periods and opportunities to resubmit. Some bowlers (particularly those who fail remediation tests multiple times) effectively end their international careers because they cannot develop a legal action — but this is a consequence of technical inability to modify the action, not a permanent ban per se. In the 1960s, before biomechanical testing, some bowlers were informally sidelined following controversy, but the modern system is more structured.
Why do some spin bowlers have more illegal action reports than pace bowlers?
Wrist-spin and off-spin bowling involve elbow and wrist positions that can produce more obvious-looking flexion than pace bowling's straighter arm arc. An off-spinner's action — where the wrist rolls dramatically at release — can visually resemble the elbow snap of a throw even when the elbow is technically within the legal threshold. Off-spinners are also typically slower than pace bowlers, giving umpires more time to observe their action closely per delivery. Additionally, some unconventional spin deliveries (the doosra, the carrom ball, the teesra) require unusual wrist positions that border on the technical definition of throwing, making reports more common for bowlers who bowl these variations. Pace bowlers are reported less because their faster arm arc is harder to visually assess for elbow straightening.