As I wrote about here, Mordecai “Three Finger” Brown was one of the greatest – and is now one of the least appreciated – pitchers ever to play the game. He utterly dominated the NL throughout the first decade of the 20th century, and played in four World Series during that stretch, winning two of them with the Chicago Cubs.
in 1906, his dominance resulted in an astounding 1.04 ERA over 277.1 innings pitched, and his 39 ERA(-) is the 5th best single-season mark in history. That year he lead the league not only in ERA, RA9 WAR and shutouts, but finished in the top 5 in WHIP, fWAR, and K/BB ratio.
I admit that I was tempted to give the OPA to Al Orth, who lead the majors in fWAR that year. Not because he lead the league in fWAR, but because his name was “Al Orth”, and nobody has ever heard of him.