 Mobley signed for Wednesday as a 17-year-old, primarily as an understudy to Peter Swan who was then first choice centre half for the England national side.Mobley's chance to play in the first team probably came quicker than expected as Swan was banned for his part in the 1964 British betting scandal.He made his debut on 4 April 1964 in a 1–1 away draw with Wolverhampton Wanderers.