In 2012, Phil Mickelson called his gambling partner and asked him to place a $400,000 bet on the Ryder Cup. A tournament Mickelson was about to play in. His partner was Billy Walters, the man ESPN once called the most successful gambler in the world. Walters says he refused. "I asked him if he'd lost his mind," Walters says. "Don't you know what happened to Pete Rose? You're looked at as a modern-day Arnold Palmer. I don't want any part of it." Mickelson hung up. The bet was never placed. In the video below, Walters describes his eight-year friendship with Mickelson, and how it ended. According to Walters, Mickelson placed about $1 billion in bets over the years and lost around $100 million. "He's made in excess of a billion dollars," Walters says. "He can do whatever he wants with his money." What Walters can't let go of is the trial. In 2017, Walters was convicted of insider trading and sent to federal prison. Mickelson had traded the same stock, made about $931,000 and agreed to pay it back. He was never charged. He also never testified. Walters believes that if Mickelson had told the jury what he had told the FBI, he never would have been convicted. After Walters got out, Mickelson walked up to him at a golf course and said he was glad to see him. That was the whole conversation. They haven't spoken since. Mickelson's response to the book: "I never bet on the Ryder Cup." Walters never said he did. He said Mickelson tried. Mickelson lost $100 million and kept his career. Walters kept the records. Did Mickelson owe Walters his testimony, or was staying silent his right?