William Henry Grigsby (born March 19, 1970) is an American former professional boxer who competed from 1988 to 2007 and held the IBF junior flyweight title twice between 1998 and 2006. He also won the WBO junior flyweight title in 2000, but was stripped of the title for failing a drug test.

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Grigsby turned pro in 1988 and lost his second professional fight, to flyweight legend Michael Carbajal who was making his professional debut. In 1998 he captured the vacant IBF light flyweight title by decisioning Ratanapol Sor Vorapin. He defended the belt once before losing it to Ricardo Lopez in 1999.^[2] In 2000 he captured the WBO light flyweight title with a decision win over Nelson Dieppa, but was stripped of the belt after the fight for testing positive for marijuana. The fight changed to no decision. He fought sporadically before capturing the IBF light flyweight title with a decision over Victor Burgos in 2005. He lost the belt in his first defense to Ulises Solís, and lost a rematch with Solís in 2007.