Hitters or pitchers who have one career year and the rest pales in comparison.
Brady Anderson--hit 50 home runs one year and the next best year was 21.
Adrian Beltre--hit 49 home runs one year and the next best was 26.
Wayne Garland--won 20 games one year and the next best was 13.
Mark Fidrych--won 19 games one year and won a total of 10 after that.
Please add to the list.