William Josiah Sumner Hammersley (25 September 1826 - 15 November 1886) was an English-born first-class cricketer and sports journalist in Victoria, Australia, one of the four men credited with setting down the original rules of the Australian rules football.
He was a prominent cricketer, a right-handed batsman and right-arm round-arm bowler, playing for Cambridge University Cricket Club, Surrey County Cricket Club and Marylebone Cricket Club. He married Jane Thirkettle in London on 23 September 1849. They had four children.
In the English Census of 1851, Hammersley and his wife Jane lived in Regents Park, London, with their 8 month old son, also William J. Hammersley gave his occupation as 'studying for the church'. By the 1861 Census, Jane was living, without William, in Hampton Wick, on the outskirts of London, with the couple's four children. Jane described herself as an 'annuitant', and had a live-in servant.
Hammersley migrated to Australia in about 1856. Upon his arrival in Melbourne he became a member of the Melbourne Cricket Club. He worked as a sports journalist for Bell's Life in Victoria and later The Australasian, where he was sporting editor until 1882, writing on cricket under the pen-name of "Longstop".
He captained the first Victorian XI to visit Sydney for an inter-colonial match in 1857 and played a few more matches until 1861. He was the first person to use the term "test match" to describe important international matches, which he did during the English cricket team's tour of Australia in 1861-62.
He was a personal friend of fellow Cambridge cricketer Thomas Wentworth Wills and helped to give momentum to Wills calls to form a football club. In 1859 he became a founding member of the Melbourne Football Club and involved in popularising the club's football code. Hammersley is also believed by some to have been instrumental in introducing Australian Rules to Sydney and in the early formation of the New South Wales Football Association.