Belfast-born Shaun turned pro with Leeds in 1969 but, after a couple of substitute appearances in the EUFA Cup, Shaun was freed by Don Revie and became one of a number of astute Joe Shaw signings, joining Chesterfield in the summer of 1974.  He filled six different positions in his first term, displaying a versatility that was to become one of his greatest assets.  He soon settled into a defensive role, but was equally at home in either full-back berth or in the centre of defence.  Although he liked to get forward and wrong-foot opponents with his trademark "O'Neill Shuffle," there were eight years between his first and second goals for the club.  His most memorable, though, was a speculative lofted cross from somewhere near the touchline that drifted in  to wreck Hereford's tilt at the highest number of consecutive clean sheets from the start of a season, in October 1984.

Freed at the end of the '82-3 relegation season, Shaun became the steward at the Saltergate Club, while playing on a non-contract basis.  Although the intention was that he would stick around a bit to help bring young players through, he remained in the first team for another three seasons.  In March '85 he received a Canon League loyalty award, and enjoyed a testimonial against Sheffield Wednesday in May of that year.  A year later he retired, with the fifth-highest number of League appearances for Chesterfield to his credit.

Shaun played local non-League football while running the Red Lion, in Brimington, before becoming a milkman, then entering the insurance business.  Out of the blue, it seemed, he was invited to become assistant to manager Ivan Golac at Dundee United.  He chucked in his job, left for Tannadice and was back in Chesterfield a day or two later, badly disillusioned at a turn of events that had seen certain verbal assurances of terms and conditions of employment fail to materialise.

He began working with Chesterfield's Community scheme in the mid-1990s, coaching schoolboy sides, and has served as the assistant coach to Barnsley's Northern Intermediate League side. After a period as coach and Manager to Staveley Miners Welfare, of the Northern Counties (East) League, Shaun took up an appointment on the staff at Chesterfield's Centre of Excellence, as Under 16 Coach, in September 2000. In recent seasons he has also jserved as assistant to his great friend Ernie Moss in his non-league management ventures.

For Chesterfield: 437+5 FL appearances, 6 goals.