Those subtle changes have paid off in a big way. In 2014, Arrieta grew into one of the best pitchers in the league, posting a strikeout-to-walk rate of better than 4-to-1 and allowing a ludicrously low five homers in 156.2 innings. Hitters couldn’t do anything with his slider (.191 batting average, .274 slugging) or his curve (.152/.229) that year.
Somehow, it was all just a prelude for the destroyer of worlds he’s become in 2015. The final step in Arrieta’s progression was to coax better results out of his sinker, which began to rival what he was doing with his nasty breaking pitches. After batting .276 against his sinker last year, opponents have hit just .199 against it in 2015. This was the culmination of Arrieta’s trifecta of velocity, command, and movement: He could now put that pitch just about anywhere he wanted at any time, the same way he commanded his devastating slider and curve. The result was a spike in Arrieta’s ground ball rate to 56.2 percent, the highest mark of his career and the third-highest among qualified NL starters.
While it’s hard enough for opponents to crack any of Arrieta’s pitches for hits, little damage has been done even when hitters do make contact. They slugged just .277 against his sinker this year … and that was the highest slugging percentage they could muster against any of his three primary pitches.
The rest of the story is one of pure dominance. But just how dominant has Arrieta been, historically?
There was Sandy Koufax, whose final eight regular-season appearances in 1965 yielded 54 innings, a 1.17 ERA, and a perfect game; he followed that by allowing one earned run in 24 World Series innings, including a series-clinching three-hit shutout in Game 7 on three days’ rest. There was Bob Gibson, who put up an 0.96 ERA in his final five starts of the 1967 season, then beat the Red Sox three times in the World Series, allowing three runs in 27 innings pitched. There was Orel Hershiser, who closed the 1988 regular season with a 59-inning scoreless streak, then won NLCS and World Series MVP honors, going 3-0 with a save and allowing five earned runs in 42.2 innings pitched.