Western Australia As a junior, Casson competed for the Western Australian Under 17 and 19 teams as well as their Second XI team, however it wasn't until the 2002–03 season when he won his first full state contract. Prior to making his
first-class debut, Casson also played for a Western Australian XI that took on the travelling
English cricket team, taking the wicket of
James Foster and finishing with figures of 1/32. With seven of Western Australia's players away on international duties, Casson made his first-class debut on 8 December 2003 against
Tasmania at the
WACA Ground. He had a quiet debut with the ball, taking 0/44 in Tasmania's first innings, but had a solid showing with the bat, scoring 35 runs in Western Australia's second innings. Casson played the remaining games of the
Pura Cup for Western Australia, however he faded with the ball towards the end of the season, finishing with 17 wickets at 39.35. The 2002–03 season also saw Casson make his
List A debut on 10 January 2003 against
Victoria at the
Melbourne Cricket Ground. He failed to take a wicket on debut, and in the three other matches he played in the
ING Cup season. Casson had a solid second season for Western Australia, taking 17 wickets at 34.11 in the
Pura Cup and 4 wickets at 33.50 in the
ING Cup, however he missed part of the season due to strained ligaments in his bowling hand. After recovering from his hand injury, Casson had mixed fortunes in the 2004-05 Australian season. He struggled with the ball and bat in the 2004-05 Pura Cup, taking 9 wickets at an average of 40.33 and scoring 36 runs at an average of 9.00. In contrast, he performed well with the ball in the
ING Cup taking 8 wickets at 17.75. The 2005–06 season was Casson's last for Western Australia, and he performed poorly, managing 17 wickets at the hefty average of 54.29 in the
Pura Cup and only 3 wickets at 41.33 in the
ING Cup. In his four years with the Warriors, Casson took 71 first-class wickets at 39.38 and 15 List A wickets at 30.20.
New South Wales In May 2006, Casson announced he was making a move east to play for the
New South Wales Blues. Although Western Australia tried to keep him, Casson felt that bowling on the more spin-friendly pitches of the
Sydney Cricket Ground would help his career. While there were doubts over whether Casson would be able to hold down a permanent place in the New South Wales team with four other spinners in the squad, he managed to play seven matches in his first season with the Blues. Despite this, he had a very poor first season, taking only 7 wickets at an average of 72.00, however his form was not helped by a shoulder injury that eventually required reconstructive surgery. Coming back from shoulder injury, Casson had an excellent 2007-08
Pura Cup season. Playing nine matches in the season, he took 29 wickets at an average of 35.13 and scored 485 runs at 60.62. He hit a career top score of 99 off 180 balls against
South Australia at the
Sydney Cricket Ground and he played a vital role in the Blues' 2007-08 Pura Cup final win. After scoring 89 in a state record seventh wicket stand with
Brett Lee, he took 4 wickets in Victoria's unsuccessful run chase, including the final wicket that won the Cup for New South Wales. His strong season was rewarded with his first
Cricket Australia contract on 9 April 2008. Despite performing well in first-class cricket, Casson struggled to make the New South Wales one-day team with
Nathan Hauritz being the first choice
List A spinner for the Blues. Casson only played one List A game and two
Twenty20 for New South Wales. He announced his retirement from all cricket in November 2011 due to his long-standing heart condition. ==International career==