Not sure this meets the criteria but David Clyde pitched at my high school while my younger siblings were there. I watched many of his games and he was dominant beyond belief. His mechanics were those of a professional pitcher and if you didn't know better you'd have sworn it was Koufax out there.
Of course, the Rangers rushed him to the majors days after the draft and he never became the player he should have been, for multiple reasons.
It took a couple of decades but his life finally turned for the better.
