Why Was Jeremy Jeffress Worse Last Year Than in All-Star 2018 Season?

Jeremy Jeffress was one of the NL’s best relievers in 2018, when he was named to the All-Star team and finished with a 1.29 ERA and 2.78 FIP. But the former Brewer followed his successful season with a 5.02 ERA and 3.96 FIP in 2019. What was the major difference between Jeffress’ disparate performances?

The one number that best explains his underwhelming 2019 is a sudden decline in whiff rate. Jeffress dominated in 2018 with a 30% whiff rate, which means he was inducing a swing and miss nearly once every three swings. But in 2019, that rate had dropped to a 20% mark that was the righty’s lowest since his tenure with the Blue Jays in 2013.

Jeffress’ subpar 2019 whiff rate is a result of several intertwined factors, some of which we’ll never truly know and others that we can quantify with ease. The normally hard-throwing righty averaged over 96 mph in 2019, but he dropped nearly two ticks last season. That alone was a major factor in the reduction of whiffs.

Another noticeable difference was that his changeup/splitter wasn’t nearly as effective, dropping from a 17% to a 9% whiff rate. That might explain why he completely abandoned the pitch for two months in the middle of the season.

Significant reduction in velocity and effectiveness is often the result of injury, which in Jeffress’ case may have been a hip problem. He didn’t report pain until the middle of August, but it was already too late by then and he was DFA’d by the Brewers on September 1. As Cubs fans saw with Steve Cishek throughout the second half of 2019, lingering hip pain can really dampen a pitcher’s performance.

“It’s not something I feel as I’m pitching. It’s the next day; stiffness and kind of tight. It just hasn’t gotten better,” Jeffress said last season. “After I pitched twice, I feel like it hasn’t gotten better, so I told the trainers I wanted to nip it in the bud and get ready for the most important part of the season, which is the back half of September.”

The degree to which Jeffress’ pain contributed to his poor numbers is unclear, but the Cubs believe the worst is behind him now that he’s had a few months to rest. With good health and perhaps a tweak here and there, Jeffress may well be able to hold down a high-leverage spot with a reworked bullpen that features quite a few unproven pitchers.