Luke Jackson might just have been the biggest surprise for the Atlanta Braves in 2019. After riding the Gwinnett shuttle and being designated for assignment in 2018, Jackson began the season with what seemed like a precarious hold on one of the final spots in Atlanta’s bullpen. After he allowed a grand slam to Rhys Hoskins on Opening Day, many figured his time in a Braves uniform was probably over. Up through that outing, it was confusing and somewhat concerning to many that the Braves were giving a bullpen spot to a replacement-level-type reliever rather than another more worthy candidate. After all, Luke Jackson had already thrown 110 innings of replacement-level relief earlier in his career, including just 0.4 fWAR in his last 90 innings or so as a Brave.
What went right in 2019?
However, replacement-level performance wouldn’t be the case. After that appearance in Philadelphia, Jackson would make 14 straight appearances (15 innings) without allowing a run. He allowed just 11 hits and four walks over that span while striking out 19.
Jackson’s turnaround was largely a result of an improved slider, which he threw 53.6 percent of the time according to Baseball Savant. That pitch helped him be extremely effective against left-handed hitters who hit just .157 against him with 44 strikeouts. In all, Jackson upped his strikeout rate to 33.7 percent and reduced his walk rate to 8.3 percent. He posted a solid 3.84 ERA to go along with a 3.24 FIP and a 2.52 xFIP. While it didn’t always seem like it, and while he faded a bit in July, Luke Jackson put together a top-30 relief season in baseball for the Braves. Among the 150 or so regularly-used relievers, he was top 30 in FIP-, top five in xFIP-, and top 20 in strikeout rate.
Even fairly early on in the year, as the bullpen was struggling, the Braves found themselves in a weird situation where the previously-marginal Luke Jackson was their one effective reliever, while their previously-great relievers really scuffled. This was never more clear than on April 27, against the Rockies: Luke Jackson came on in the seventh in relief of Mike Foltynewicz, with the Braves up two, none out, and the tying runs in scoring position. He allowed an RBI groundout but then retired the next two batters to preserve the lead. He then went 1-2-3 against the heart of Colorado’s order (Trevor Story, Daniel Murphy, Nolan Arenado). The Braves would then go on to lose the game after Jackson left as A.J. Minter and Dan Winkler turned a one-run lead into a four-run deficit.
One particular strength for Jackson was ability to go more than just an inning. In 10 of 70 outings, he got four or more outs; in only one of those did he allow any runs. Only two of those 10 outings came in garbage time, meaning that Jackson threw multiple high-leverage innings more than a few times in 2019.
What went wrong in 2019?
Jackson’s ERA rose to 5.65 in the second half over his final 28 2/3 innings. However, a 3.91 FIP and a 2.51 xFIP indicate that he was a bit unlucky.
In fact, “a bit unlucky” doesn’t quite do anything justice. In the Statcast era (since 2015 began), only five pitchers with more innings thrown in a season than Jackson have had greater gaps between their wOBAs and xwOBAs. Jackson finished the season with a .386 BABIP, which is the highest mark for a “qualified” Braves reliever since... 1871. The contact he allowed should have gone for hits 33 percent of the time, a pretty decent mark; instead, it went for hits a horrific 42 percent of the time. It’s no wonder that Luke Jackson often looked haunted on the mound after another dribbler got through the infield — the batters couldn’t have rolled much of their contact any more fortuitously than what ended up happening to him again and again.
Probably the most obvious ghastly coup de grace in this regard was May 21, against the Giants. Luke Jackson would come into the game with a two-run lead, and would leave the field with the Giants securing a walkoff victory. However...
This was, of course, the whole point of Luke Jackson’s rotten 2019 experience — he had his worst on-paper outing of the season in a game where he allowed four singles, none above 93 mph off the bat.
Brian Snitker used Jackson as his closer early on and primarily in middle relief after the arrival of Chris Martin, Shane Greene and Mark Melancon at the trade deadline. He made three appearances in the Division Series against the Cardinals allowing six hits and three earned runs in 2 2/3 innings.
What to expect in 2020?
Given the volatile nature of relievers, Jackson will be interesting to watch in 2020. He should go to Spring Training in much better shape than previously in his career. His slider was his money pitch in 2019 and he should continue to rely on it heavily. Still, we have seen relievers in recent years turn in solid seasons and then fall off the cliff the very next year. It will be interesting to see if Jackson can build off of 2019. Basic regression and justice suggests Jackson should get some measure of payback for his silly 2019 results, but there’s no guarantee that he will actually be as effective next year as he was this past season.