From the Handbook: Tyler Duffey's pitches

Tyler Duffey went
9-12, 6.43 in 2016.

Back to mining the Bill James Handbook, this time from the section on pitchers and their offerings:

One of the many things that went wrong with the 2016 Twins was the marked decline in effectiveness of starting pitcher Tyler Duffey. He was one of their better starters down the stretch in 2015; he was not good in 2016.

I had two theories, not mutually exclusive, about what was wrong with Duffey:

• The sharp increase in his 2015 workload caught up to him in 2016
• The insistance of pitching coach Neil Allen that everybody on the staff throw a changeup had Duffey using a mediocre pitch too often

A variation of that latter: Trying to master a change detracted from his fastball command.

These numbers don't confirm any of those theories. But Duffey's pitch selection changed a bit this year from 2015;

2015: 58 percent fastballs, 40 percent curves, 2 percent changeups
2016: 54 percent fastballs, 39 percent curves, 7 percent changeups.

Assuming 100 pitches per start, that's just one less curveball per game. But he certainly essayed more changeups, throwing five more per game. His average fastball velocity was essentially the same (actually increased by 0.2 mph).

Seven changeups per game doesn't seem excessive, and anecdotally, I don't seem to recall him getting burned on the pitch. I'm more inclined to blame a deterioration of his fastball command. Whether that came from his workload increase or experimenting with a new pitch -- or both -- I don't know.