Former NBA star Tracy McGrady is trying to make it in baseball as a pitcher. The ESPN highlight is below, but more video of his pitches can be seen at this Deadspin compilation.
He was clocking in the low to mid-80's with his fastball. Not sure if he's still building up arm strength, but even with the potential downhill plane he can generate with his 6'8" frame, that's not really going to cut it.
Still, moving from almost any of the other major U.S. sports to baseball is unbelievably difficult because so many of its skills, especially hitting and pitching, are so vastly different and specialized. Think about most major league pitchers and how terrible they look when trying to bat, and then recall that many of those players were the best player on their high school team, both as hitters and pitchers, and you realize just how complex a skill that is. It's one reason Bo Jackson was such a legend, and deservedly so.
McGrady's 6'8" frame and long arms make pitching even more difficult because of the length of his lever. Recall how hard it was early in Randy Johnson's career for him to control his pitches. It's one reason you don't see a ton of super tall pitchers in MLB.
So McGrady is likely to fail, but it's a good story.