William Scott Sullivan (born March 13, 1971) is an American former professional baseball player.

From 1996–2003, Sullivan was one of the Cincinnati Reds's most durable relief pitchers, and was looked upon as a clubhouse leader.

His best season came in 1999, a year in which the Reds won 96 games but did not make the postseason after losing a one-game playoff to the New York Mets.

That season, Sullivan set or tied career highs in saves (3), appearances (79), innings pitched (113.2) and ERA (3.01).

Like many "submarine pitchers" (as they're sometimes called), he developed back problems, which resulted in multiple trips to the disabled list toward the end of his career.