When Danny Duffy first arrived in the big leagues, he was electric. As a guy, he’s naturally laid back — perhaps a product of having grown up in southern California — but he used to throw really hard. Unfortunately, the velocity didn’t necessarily translate to success. Duffy lacked real command of his repertoire. As the left-hander put it to me recently, he “had no idea where the ball was going.” He threw mostly just four-seam fastballs and a curve.
Duffy has evolved pretty considerably since his rookie season in 2011. It’s not that he’s just a command guy now — he still throws hard — but a lot has changed over the last few years. With more than a month left in the season, Duffy has already recorded the highest WAR figure (2.9) of his career.
What happened? What allowed him to refine his command, to establish a more ideal pitch mix? Duffy recently helped answer those questions, relating all the “aha” moments that led to a completely different, and much more successful, arsenal — an arsenal I address pitch by pitch in what follows.
The Fastball
This year is the closest Duffy has ever come to throwing more sinkers than four-seamers. There’s always a ground-ball benefit — “I started getting more ground balls, more weak contact,” said Duffy, who is currently enjoying the highest ground-ball rate of his career — but this change was more about command than outcomes on balls in play.

When Duffy first came up, the refrain was that he’d go as far as his command would take him. “I thought I had to be so fine when I was younger, because I struggled with the strike zone so much,” Duffy remembered. “Then I figured out that it was all about repetition. You can’t expedite it; experience will give it to you.”
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