South African off-spinner Johan Botha's 'doosra' delivery has been declared illegal by the International Cricket Council but his off-break and arm-ball were cleared after biomechanic tests.
"An independent test has found the 'doosra' delivery of South Africa bowler Johan Botha to be illegal and the player has been warned against bowling that particular delivery in international cricket," the ICC said in a statement.
"A comprehensive analysis revealed that his action for the 'doosra' exceeded the 15-degree level of tolerance permitted under regulations.
"But the same assessment found that Botha's off-break and arm-ball deliveries were bowled within the tolerance level and so the 27-year-old can continue to bowl those types of deliveries at international level," it added.
The biomechanic tests were conducted by Prof. Bruce Elliott, member of the ICC's Human Movement Specialists panel, at the University of Western Australia, Perth on April 30.
The analysis showed that the amount of elbow extension in Botha's bowling action for both his off-break delivery and arm-ball was within the 15-degree level of tolerance.
"The mean elbow extension was 12.2 degrees for the off-break and 11.1 degrees for the arm-ball with no single delivery of those types proving to be illegal," the ICC statement said.
However, the analysis showed that the amount of elbow extension in Botha's 'doosra' delivery was 26.7 degrees with no single delivery proving to be legal.
Prof. Elliott has advised Botha to review his bowling action on a regular basis to ensure his elbow flexion levels are minimised and kept within legal limits.
Botha had been reported after the fourth ODI between Australia and South Africa in Port Elizabeth on April 13 by the on-field umpires Brian Jerling and Asoka de Silva, along with third umpire Rudi Koertzen.
Botha can apply for a re-assessment of his 'doosra' action after he has modified it. Botha also has the right to appeal against Prof Elliott's conclusions to the Bowling Review Group.
Should he choose to appeal, the South African must lodge a written notification with the ICC within 14 days of receiving the report.
Botha has been named South Africa's vice-captain for the Twenty20 World Championship in England next month and he has been cleared to play on the condition that he does not bowl the 'doosra'.
