Sydney Raper joined and made his first grade debut for
Newtown in 1957 as an eighteen-year-old. Despite becoming a much lauded lock forward, in his 1957 debut season with the Newtown “Bluebags” (as the team was known then) Raper played in the second row in all of his first grade appearances except one when he played at five-eighth. And throughout the 1958 season for Newtown first grade he played at five-eighth except for one game at centre and one game in the second row. During the 1958 season he had his first taste of representative football against elite opposition when selected to play for combined Sydney against the visiting Great Britain team and then for New South Wales Colts against the British tourists. In both these representative games Raper played at lock forward and opposed one of the great locks of that era in Britain’s
Vince Karalius. In 1959 Raper joined
St George as a lock forward and in this position he became an international rugby league star. His legendary cover defence and ball skills saw him acknowledged during his playing career as the best loose-forward the world had ever seen. He played in eight
Grand final wins with St George between 1959 and 1966. In 1959–60 he made the first of his three
Kangaroo tours, scoring a try on debut in the third Test loss vs Great Britain at Wigan. For the next ten years he was rarely, except for injury, out of the Australian Test team. Raper's performance in the second Test of the 1963 tour at Swinton which saw the Kangaroos register the biggest win in Anglo-Australian Test history and become the first Australian touring team in fifty years to win the
Ashes was pivotal. In the 50–12 victory, Raper had a hand in the first seven tries in the opening 25-minute routing and he gave the final pass in four of them. In his third Kangaroo tour of 1967–68 Raper suffered a cheekbone fracture in the opening 16–11 Test loss causing him to miss the second Test won by Australia to keep the series alive. Captain-coach
Reg Gasnier had broken a leg in the first Test so Raper upon his return to fitness, was deputised and earned the ultimate Australian
rugby league honour captaining his country in the 11–3 win over Great Britain played in icy conditions on a frozen ground in Swinton on 21 October 1967. Raper went on to captain Australia in the first and third Tests against France in 1967–68. Queenslander
Peter "Pedro" Gallagher was the captain for the second Test when Raper was injured. For the 1968 World Cup Raper captained Australia in their four undefeated games of the tournament including the 20–2 victory against France in the final at the Sydney Cricket Ground. Raper's last season with St George was in 1969 as captain-coach. In 1969 he appeared as a guest player for
Auckland in a match against the
New Zealand national rugby league team to mark the
New Zealand Rugby League's diamond jubilee. Raper was awarded Life Membership of the St. George Dragons club in 1971.
Newcastle Raper played three seasons with the
Western Suburbs Rosellas in the Newcastle competition from 1970 to 1972. He captain coached the club and took them to victory in the 1970 grand final. He finished his playing career with Kurri Kurri from 1973 to 1974. After five games of the
1978 NSWRFL season and internal turmoil leading to the resignation of first-grade coach
Paul Broughton, Raper took over as coach of the
Newtown Jets in a caretaker capacity. ==Post football life and accolades==