Rugby league club Hull had different ideas about Sullivan and gave the young man, who boasted phenomenal speed, a chance to play rugby league. In his début for Hull, Sullivan had an outstanding game and gained the support of the Hull club and city. Sullivan became known for his exceptional speed. His upper-body was deceptively strong which gave him excellent cover defence. Despite his knees requiring constant attention and further operations, he played a total of 352 games for Hull, scoring 250 tries. In his 213 games for Hull Kingston Rovers he scored 118 tries.