Legal vs Illegal Bowling Actions Explained

A legal bowling action in cricket requires the bowler's arm to be straight at the point of delivery — or within a defined tolerance of straightening. The historical rule was that any extension of the elbow joint during the delivery swing was illegal ('throwing' or 'chucking'). Scientific study has since shown that virtually all bowlers straighten their elbow to some degree during a delivery, leading the ICC to introduce a tolerance threshold rather than a zero-tolerance rule. Understanding the bowling action rules requires grasping the biomechanics of human arm motion and how cricket regulators have adapted the Law to match scientific reality.

The Law: What Makes a Delivery Legal

Under Law 24 of the Laws of Cricket, a delivery is illegal if the bowler's arm extends at the elbow joint by more than 15 degrees at the moment of delivery. The ICC introduced this 15-degree tolerance in 2004 following biomechanical research that showed most bowlers — including those never suspected of throwing — naturally extend their elbow by up to 10–14 degrees due to the speed and force of the delivery motion. The 15-degree threshold was set to cover this natural range while still prohibiting bowlers who extend far beyond the biomechanically natural motion. Bowlers who extend their elbow beyond 15 degrees are considered to be throwing, and their action can be reported and banned.

How ICC Tests a Suspected Bowling Action

When an umpire or match referee suspects a bowler's action, they file a report. The ICC then requires the player to attend an accredited biomechanics centre (typically at one of three globally approved facilities) for official action testing. At the facility, the bowler bowls in a controlled environment with high-speed cameras and motion-capture sensors measuring the exact degree of elbow extension across different delivery types (pace deliveries, variations, off-spinners). If the results show extension beyond 15 degrees for any specific delivery type, that delivery type may be suspended while the bowler re-trains. The bowler must then retest before resuming the banned delivery type at international level.

Famous Illegal Action Controversies

Muttiah Muralitharan of Sri Lanka was called for throwing by Australian umpire Darrell Hair in 1995 — one of cricket's most controversial umpiring decisions. Biomechanical testing showed Muralitharan's unusual wrist rotation, combined with a congenitally bent elbow (his arm could not fully straighten), created the visual impression of throwing without violating the Laws. The controversy consumed cricket for years. More recently, Saeed Ajmal (Pakistan) and Shoaib Malik were both suspended pending action tests. Bangladesh fast bowler Taskin Ahmed was suspended during the 2016 T20 World Cup after his action was reported during the tournament. Off-spinner Murali's case ultimately prompted the ICC's 15-degree rule, resolving the biomechanics dispute scientifically.

The Visual Challenge of Umpiring Bowling Actions

Umpires face a genuine difficulty: detecting elbow extension beyond 15 degrees with the naked eye at delivery speeds of 120–145 km/h is practically impossible. Research shows umpires can only reliably detect extension beyond 20 degrees visually. Below 20 degrees, visual detection is inconsistent. This means many borderline actions at 15–20 degrees are never reported. The ICC relies on a combination of umpire reports (primarily triggered by dramatic visual cases), broadcaster footage alerts (if TV analysis highlights a suspicious delivery in slow motion), and official channel reports from match referees. The system is imperfect but has reduced major throwing controversies compared to the highly contentious pre-2004 era when the standard was absolute and undefined.