He started shooting after receiving an air rifle from his grandfather, a hunter, and following his older brother.[4] Being a junior, he was labeled unperspective, as he stated in 2021.[4]
Nevertheless, in 1993, Kostelecký won a bronze medal at the European junior championships in his home Brno. He won junior world championships in 1995 in Nicosia, where he finished second in the European championships in 1995, starting his senior championships medal collection. In 1996, he participated in his first Olympics, finishing 31st in the qualification round behind both his compatriots (Jiří Gach finished eighth and Pavel Kubec 13th).[5]
In 2002 he became European champion in Lonato taking advantage from the basic round result of 122 and keeping off Marco Venturini in the final.[6] It was the first individual European gold in trap for any Czech shooter. He also finished second in the 2006 ISSF World Cup final.[7]
April 1, 1994 June 9, 1995 June 11, 1996 July 23, 1998 August 10, 2005 October 5, 2006 May 15, 2009 September 6, 2011 August 6, 2012 April 18, 2013 October 16, 2014 August 15, 2015 March 19, 2019 April 9, 2019 June 2, 2021 September 24, 2023
