Madison Bumgarner Heads to Phoenix

On Sunday, it was reported that the Diamondbacks had signed long-time Giant Madison Bumgarner. The pitcher that had never posted an ERA exceeding 3.37 heading into the season ended up suffering the worst results of his career, posting a 3.90 mark, even as his strikeout and walk rates rebounded to pre-2018 levels. Now he departs one of baseball’s most pitcher friendly venues. How much will the park switch affect his performance? Let’s consult the park factors.

Surprisingly, the parks sport identical singles and doubles factors. That’s good news, as a change there could have affected Bumgarner’s BABIP. For his career, he owns a .284 mark, which is well below the league average, despite a league average batted ball distribution. How much of that suppressed mark is due to the Giants defense or some ability to induce weak contact, it’s difficult to say. But right now, the Giants are projected for a slightly better defense than the Diamondbacks, who we have right now for a -0.9 Fld rating, which is essentially league average.

Chase Field is the second best park in baseball for triples, but Bumgarner is coming from another park that dramatically inflates triples. That said, for the lowest frequency hit type, this shouldn’t have a serious effect on his ERA.

The big swing that actually matters comes from the home run park factors. Oracle Park is easily the most pitcher friendly park for homers, which explains Bumgarner’s home/away HR/FB rate splits, where he has posted a home HR/FB rate three percentage points lower. He’ll now be pitching in a home park that is almost exactly neutral. I’m real curious to see where his HR/FB rate ends up this year. It’s sat in a narrow range between 10% and 12.9% every season since 2014, which is pretty remarkable given how much that rate tends to fluctuate.

The strikeout and walk rate factors are very similar, with Chase slightly boosting walks, while being marginally better for strikeouts. The effects are probably enough to offset one another, but the differences between the parks is probably too small to matter.

The line drive and pop-up factors diverge a bit more, with Chase inflating line drives, but also boosting pop-ups. Since line drives occur more frequently than pop-ups, and the jump here is more significant than the jump in pop-ups, this appears to be a net negative for Bumgarner’s BABIP.

Overall, Chase is about neutral for FIP, versus pitcher favorable for Oracle, and exactly neutral overall, versus favorable for pitchers in Oracle. Between the BABIP increase due to the higher line drive rate and worse defense, and the increase in homers, the park switch is a clear negative and should reduce his projected fantasy value. For a guy who has consistently outperformed his underlying skills, it’s scary to think what might happen now that he’s out of one of baseball’s most pitcher friendly home parks.