An Illegal Bowling Action is where a player is throwing rather than bowling the ball. This is defined by the ICC as being where the player’s elbow extends by an amount of more than 15 degrees between their arm reaching the horizontal and the ball being released. Match Officials in international cricket use the naked eye and their cricketing experience to decide whether they believe a player may be using an Illegal Bowling Action and, if so, they will submit a report.
The player is then tested at an ICC Accredited Testing Centre, using state-of-the-art technology and supervised by experts in the science of human movement. This testing process provides an answer as to whether the player is in fact using an Illegal Bowling Action and, if so, they will be suspended from bowling until they have modified their bowling action and undertaken another test successfully.