While playing for the Vale he appeared in two Scottish Cup Finals, in 1883 and 1885, but had the misfortune to be on the losing side to local rivals on both occasions.
The Scottish Football Association declined to alter the date of the game for this and other excusal reasons proposed by Vale of Leven, and as a result the club refused to participate in the match out of respect for Forbes and his family[4] and forfeited the trophy to Queen's Park after a vote on the issue.
In March 1887 he was a member of the Rangers team that was beaten by Aston Villa in the FA Cup semi–final at Nantwich Road, Crewe.
[8] Forbes made his international debut on 26 January 1884 at the Ulster Cricket Ground, Belfast against Ireland; Scotland won 5–0.
In an article in "The Scottish Referee" in March 1902, it was said of Forbes that in his youth, 'so fast was he that he lost command of the ball, over running it, and waiting for it to come to him, and not vice versa'.
[citation needed] However, his gift of speed and natural athleticism led him to adopt a roving commission in the role and his critics castigated him for being 'all over the shop'.