The headline claims he resigned, but when you read his comments, it's clear the Academy left him with no other choice.
At the New York Times, "Will Smith Resigns From Academy After Slapping Chris Rock at Oscars":
The producer of the telecast said that Smith had been asked to leave after slapping Rock, and that he had urged officials not to “physically remove” him. LOS ANGELES — Will Smith, who slapped the comedian Chris Rock at the Oscars, said Friday that he was resigning from the Academy of Motion Picture Arts and Sciences, saying that he had “betrayed” its trust with conduct that was “shocking, painful, and inexcusable.” The sudden announcement came late Friday afternoon, days after the Academy had condemned Mr. Smith’s actions and opened an inquiry into the incident. “I have directly responded to the Academy’s disciplinary hearing notice, and I will fully accept any and all consequences for my conduct,” he said in a statement on Friday. “I deprived other nominees and winners of their opportunity to celebrate and be celebrated for their extraordinary work,” he said in the statement. “I am heartbroken.” He said that he would “accept any further consequences the board deems appropriate.” “Change takes time,” he concluded, “and I am committed to doing the work to ensure that I never again allow violence to overtake reason.” Now that he has resigned, Mr. Smith will no longer have access to academy screenings and events. He will also not be able to vote in the Academy Awards. However, he could still be nominated for an award, since being a member is not a requirement for eligibility. Mr. Smith’s resignation came roughly 12 hours after Will Packer, the lead producer of the Oscars telecast, spoke publicly about the episode for the first time. In an interview with Good Morning America” on ABC, the network which also broadcasts the Oscars, Mr. Packer said that after Mr. Smith had been asked to leave the ceremony, he urged the Academy leadership not to “physically remove” him from the theater in the middle of the live broadcast. Mr. Packer said he had learned from his co-producer, Shayla Cowan, that there were discussions of plans to “physically remove” Mr. Smith from the venue. So he said he immediately approached academy officials and told them that he believed Mr. Rock did not want to “make a bad situation worse.” “I was advocating what Rock wanted in that time, which was not to physically remove Will Smith at that time,” Mr. Packer said. “Because as it has now been explained to me, that was the only option at that point. It has been explained to me that there was a conversation that I was not a part of to ask him to voluntarily leave.” In the interview, Mr. Packer also said that Mr. Rock’s joke about Jada Pinkett Smith’s hair was unscripted “free-styling.” “He didn’t tell one of the planned jokes,” he said of Mr. Rock. Someone close to Mr. Rock who asked to speak anonymously because the Academy’s inquiry into the incident is ongoing said that Mr. Rock was never asked directly if he wanted Mr. Smith removed. Had he been asked, it was not clear how Mr. Rock would have responded, the person said. Mr. Rock was only asked if he wanted to press charges, and he said that he did not, the person said...