[2] He married Ethel Breeze in June 1913 and had four children, the oldest being future footballer and manager Joe Mercer.
[2] On 16 December 1914, four months after the outbreak of the First World War and the day after the Football Battalion of the Middlesex Regiment was established, Mercer and Nottingham Forest teammates Tommy Gibson and Harry Iremonger travelled down to London to enlist.
[2] At the front, Mercer was promoted to sergeant,[5] but sustained wounds to the head, leg and shoulder and was captured by the Germans in Oppy on 28 April 1917.
[2][6] He was held in camps at Douai, Bad Langensalza, Giessen and Meschede and returned home in January 1919.
[2] In the post-war years, Mercer attempted to resume his football career and continued working as a bricklayer.