In August 2013, Byrne signed a two-year Category B rookie contract AFL club Carlton.[1][7]
Byrne made his senior AFL debut in Round 3, 2015 against Essendon at the MCG; however, after a hamstring injury in that game, he missed the remainder of the season, playing only a couple of games for Carlton's VFL-affiliate, the Northern Blues.[8] He became a regular in the team's backline in the early part of 2016, playing 11 of Carlton's first 14 games before rupturing his right anterior cruciate ligament, an injury which caused him to miss the rest of the 2016 AFL season.[9]
In October 2018, Byrne informed Carlton Football Club of his decision to retire from AFL football and to return to Ireland.[2] Byrne stated that he had fallen "out of love" with the Australian code and wanted to return to Gaelic football.[3]
Return to Gaelic football
After returning to Ireland, Byrne resumed his Gaelic football career with the St Mochta's club. Shortly after resuming the game he dislocated his ankle in the Louth Intermediate Football Championship final (which St Mochta's won after appearing there for the first time since 1981).[3] This injury caused Byrne to miss another season, and was initially thought to be career-threatening.[3] He recovered with the aid of reformer pilates (which he had first used while recovering from injury in the AFL) and subsequently began a pilates business in his home village of Louth, County Louth.[3]
Byrne was selected to play for Louth again and joined the county's senior football panel in 2020[10]
^ abcdDe Bolfo, Tony (15 August 2013). "International rookie Byrne signs with Blues". Carlton Football Club. Retrieved 15 October 2013. As Hughes said: 'The boys already call him Casey – a nickname he inherited years ago because his younger sister couldn't pronounce 'Ciaran.