When was the last time a pitcher in Major League Baseball was caught throwing a spitball?
If you mean a ball with some sort of gooey substance, it was probably Gaylord Perry in 1982. It was the first and only time he was caught in a game, in his 21st season, even though he absolutely notorious for using the spitball. If you mean any doctored ball, Joe Niekro was thrown out in 1987 for having a nail file, which when used on a ball, the ball is usually still called a spitball (unless there’s something I don’t know). I think those might be the last times.