Free Agent Starters and Rotation Candidates: By The Numbers (Part I)
As we near the two week mark before pitchers and catchers report in Fort Myers, we're starting to see signs that this painfully frigid free agent market may be finally thawing. The Brewers staked their claim on a crowded NL Central with two big outfield acquisitions last week, and rumors abound that Yu Darvish is closing in on a decision that might open the free agent starter floodgates.
While we wait to hear whether Darvish picks the Twins or sends the front office scrambling for Plan B, let's take a look at how the top four free agent starters – Darvish, Jake Arrieta, Lance Lynn and Alex Cobb – stack up against the existing Twins rotation candidates by the numbers. Today we'll start with rate stats, and I'll follow up with a "Part II" that takes a deeper look at the major WAR and projection models.
I imagine every Twins Daily reader is familiar with the drawbacks of both ERA and FIP. ERA holds the pitcher completely responsible for every ball in play, ignoring defense, ballpark factors and dumb luck. FIP clears the pitcher of any responsibility on balls in play that don't leave the ballpark, ignoring quality of contact on those balls in play.
Enter this author's new favorite pitching stat: Statcast's new xwOBA metric. You can find a detailed description at the previous link, but you could say that xwOBA takes FIP to the next level: maintaining the pitcher's responsibility for strikeouts and walks while also giving pitchers due credit (or penalty) for their quality of contact beyond just home runs.
Ervin Santana is a great case study here. Erv's 2017 ERA was stellar, but his FIP suggests that it was helped out quite a bit by some combination of defense, ballpark factors and luck. xwOBA helps us cut through the noise here by showing that Santana's overall production (.292 vs. .320 lg avg) was more in line with his ERA (3.28 vs 4.49) than his FIP (roughly lg avg).
Yu Darvish's numbers, especially in the second half, tell a similar story. xwOBA suggests that he was far and away the best of the available free agent starters in spite of his inflated ERA, and that his second half was terrific despite some of the traditional results suggesting he faded. Perhaps this, and his strong early starts in the playoffs, suggest that his World Series collapse was in fact the result of pitch tipping rather than an overall fade in production.
Arrieta's second half may be even more interesting. His ERA drops substantially in the second half, and while his FIP suggests that it may have been more luck than production, his xwOBA reinforces that he was indeed generating significantly better quality of contact to go with his continued strong strikeout and control rates.
With Lance Lynn and Alex Cobb we can say with some certainty that either would have slotted well ahead of any Twins pitchers not named Santana or Berrios in 2017, but let's take a closer look at the numbers. Nick recently applauded Lynn on Twitter for his consistency and the numbers back him up here, particularly looking at xwOBA which suggests that an inflated 2017 FIP may not be that concerning. With Cobb, many have pointed to his hot second half as a positive, but his FIP remained essentially the same and his xwOBA actually regressed in the second half, suggesting his second half surge may have had a fair amount of luck attached to it.
What else jumps out at you in these numbers? Mejia's second half? May's strong 2015 xwOBA as a starter?