In Round 19 of the 1988 NSWRL season, Sing made his first grade debut in Balmain's 16–22 loss to the Western Suburbs Magpies. He did not feature again in first grade for the Tigers until 1991, when he played 13 games. In 1992, he moved to the Eastern Suburbs Roosters but struggled for game time, playing just 14 games over three seasons.
In 1995, he joined the newly established North Queensland Cowboys, playing in their inaugural game against the Sydney Bulldogs. Sing played his first full season of first grade for the Cowboys in 1995, playing 20 games. At the end of the season, he won the club's Player of the Year and Players' Player awards.[4] In 1996, he played 15 games for the club before departing at the end of the season.