After the July 23rd Oakland "Day on the Green" show, a Bill Graham staffer was severely beaten for asking Peter Grant's [Zeppelin's manager] kid to return signage, torn down from dressing room doors. After an initial kick in the groin by Drummer, John Bonham, Zeppelin "security forces", including Grant, locked the BGP employee in a trailer and savagely beat him. Led Zeppelin's second Oakland show took place only after Bill Graham signed a letter of indemnification absolving Zeppelin from responsibility for the previous night's assault. The letter, signed by Graham under duress and with his left hand, was considered invalid, and Bonham, Grant and two security thugs were arrested.