Summersby began his playing career at Millwall, initially as a junior before signing as a professional in March 1952, but did not fully establish himself in the first team until 1957.[3] In December 1958,[2] he signed for Crystal Palace then playing in the Fourth Division in its inaugural season. He quickly became a first team regular and put together a sequence of 126 consecutive appearances, many of them alongside Johnny Byrne.[3] In October 1959, Summersby scored four goals in Crystal Palace's biggest-ever league win; a 9–0 home victory over Barrow.[4]
In the 1960–61 season, Palace achieved promotion to the third tier and Summersby was ever present, making 46 appearances, scoring 25 goals,[5] which is still (as of September 2014) the fourth highest seasonal goals total in Crystal Palace Post-War history. Only Byrne the same season (30), Andrew Johnson in 2003–04 (28) and Glenn Murray in 2012–13 (30) have scored more goals.[6] The next season, Summersby made 42 appearances, scoring eight times,[7] but in 1962–63 only appeared 17 times (in the first half of the season) and scored twice.[8] At the end of that season, in May 1963, he transferred to Portsmouth, rejoining former Palace managerGeorge Smith.[3] However, after only 12 games for Portsmouth, over two seasons,[9] Summersby moved on to non–league football with Chelmsford City and later Hillingdon Borough.[3]