Within minutes, a separate off-stage incident involving Graham's security man Jim Matzorkis, who allegedly slapped Grant's 11-year-old son Warren over the removal of a dressing room sign, escalated into an all-out brawl that resulted in Matzorkis being taken to hospital after being beaten by Grant and Bindon. The band, except John Bonham, were performing on stage and were unaware of what was transpiring backstage. Led Zeppelin's second Oakland show took place only after Bill Graham signed a letter of indemnification absolving Led Zeppelin from responsibility for the previous night's incident. However, Graham refused to honour the letter because, according to his legal advice, he was under no obligation to agree to its terms.