His first experiences of track and field competition were as a junior high jumper and John Anderson, the referee for the UK television series "Gladiators" and coach of former world record holder Dave Moorcroft, urged him to focus on athletics. Training at Corby Athletics Club, he began competing in the decathlon and 110 metres hurdles and he became the No. 1 ranked under-20 British athlete in both disciplines. At the Amateur Athletic Association (AAA) under-20s championships in 2003, he won the decathlon. His first major junior competition was the 2003 European Athletics Junior Championships, where he finished fifth in the 110 m hurdles final. He competed at the 2004 AAA meeting and finished third in the hurdles, behind Robert Newton and Paul Gray. At the 2005 European Athletics U23 Championships, Sharman was just outside the medals with a fourth-place finish. A shoulder injury that year had impaired his javelin throwing ability and he made the decision to abandon the decathlon to focus solely on hurdling.