Complex sentence: Dieppa was declared winner by unanimous decision at first, but following the event Grigsby tested positive for cocaine after the fight, the WBO declared the fight a no contest and Dieppa was stripped of the championship.
Split into simpler sentences: Dieppa was declared the winner by unanimous decision at first, but Grigsby tested positive for cocaine after the fight. The WBO declared the fight a no contest and Dieppa was stripped of the championship.