Strikeforce: Shamrock vs. Diaz was a mixed martial arts event held by Strikeforce on April 11, 2009 at the HP Pavilion in San Jose, California. It was the first event promoted by Strikeforce after their acquisition of assets from the defunct EliteXC promotion through its parent company ProElite. It aired on the Showtime cable network and online through Strikeforce All Access.Gus Johnson, Mauro Ranallo and Pat Miletich were commentating during the broadcast and Jimmy Lennon Jr. was the ring announcer. The official attendance was announced to be 14,409.