He played club level rugby union (RU) for Wakefield Balne Lane RFC (the team was runner-up in rugby union's Yorkshire Cup in both 1905 (against Harrogate RUFC) and 1906 (against Castleford RUFC (in Castleford, Wakefield)), and representative rugby league (RL) for Yorkshire, and at club level for Wakefield Trinity (captain), as a stand-off, or scrum-half.
[1] Harry Slater won cap(s) for Yorkshire (RL) while at Wakefield Trinity.
Harry Slater played stand-off, and was captain in Wakefield Trinity's 17−0 victory over Hull F.C.
in the 1909 Challenge Cup Final during the 1908–09 season at Headingley, Leeds on Tuesday 20 April 1909, in front of a crowd of 23,587.
In addition, prior to the 1949–50 season, the archaic field-goal was also still a valid means of scoring points.