Jay Jackson is emerging as important piece in Brewers bullpen

After struggling for most of the season, the Milwaukee Brewers bullpen has come together at just the right time. The relief unit stumbled to a 4.64 ERA and 4.41 FIP through the end of August, which ranked 19th and 17th among all MLB clubs, respectively. In September, however, the bullpen has posted a fantastic 2.82 ERA (3rd) and 3.38 FIP (2nd) while gobbling up 99 innings.

Part of the reason behind the sudden turnaround is that we’re in the midst of #Craigtember, meaning Craig Counsell can work his magic with expanded rosters by putting every reliever in the best positions to succeed (and by pulling them quickly if it’s clear that they don’t have it on that particular night). The biggest reason is that several relievers have stepped it up when they’ve needed to. Josh Hader remembered that he has a slider and has bounced back from his post-All Star break struggles. Counsell and his staff have come up with an effective rest plan for Freddy Peralta, and he has responded by dominating to the tune of a 1.93 ERA and -0.21 FIP. Brent Suter has returned from Tommy John surgery and allowed just one run in 14.1 innings of work. Perhaps the most attention has gone to Drew Pomeranz, and rightfully so. The big lefty has adopted a “let it rip” mentality, riding a significant spike in fastball velocity to a whopping 43.8 K% since being acquired at the trade deadline.

However, there’s another reliever who has quietly been putting up solid numbers lately: Jay Jackson. Furthermore, he has shown signs that he could soon emerge as one of the club’s more important relief arms.

The 31-year-old rookie’s 4.40 ERA (99 ERA-) doesn’t stand out. However, his 3.95 FIP is seven percent better than league average. Deserved Run Average, arguably the most comprehensive pitching metric publicly available, believes that Jackson has done great work out of the bullpen. His 3.80 DRA is about 23% better than the league-average DRA. He also boasts a strong 3.09 SIERA.

What really stands out about Jackson is his swing-and-miss stuff. He does not have enough innings to qualify on FanGraphs’ pitching leaderboards, but here’s where he ranks as of Monday among the 316 relievers who have thrown at least 20 innings this season:

• 13th in strikeout rate (37.7%)
• 7th in swinging strike rate (18.0%)
• 4th in opponent contact rate (62%)

Small sample size be darned, that’s pretty impressive, and it should be noted that getting lots of empty swings isn’t anything new for Jackson. During his three-year stint in Japan, he punched out 192 in 176.1 innings of regular-season action. In Triple-A San Antonio this season, he struck out 54 in 40 innings, helping him achieve an elite 1.33 ERA and eye-popping 22.8 DRA- in the offensively-dominated Pacific Coast League.

Like most relievers in today’s game, Jackson throws hard. His average fastball velocity is 94.3 miles per hour, and he has topped out at 96 miles per hour. However, that’s not the reason why he’s been racking up K’s. Rather, the righty’s slider is his money pitch, and he utilizes it as his primary offering. Jackson throws the breaking ball 55.5% of the time, and it’s pretty nasty.

The movement on the pitch, combined with Jackson’s deceptive delivery, have made it difficult for opposing hitters to pick up. They’ve come up empty on 45% of their swings against the slider, hitting just .161 with a .208 wOBA and .262 xwOBA against it. Despite his limited number of innings at the big-league level this season, Jackson’s slider has been worth +6.7 runs per FanGraphs, which ranks 26th out of the 690 relievers to throw a pitch in the majors this season.

The results of Jackson’s nasty stuff have started to show recently. He bounced between Triple-A and the big league team for most of the summer, posting a 5.79 ERA in that span. On August 18th, Jackson was called up for good, and he’s put up impressive numbers since that time. In his last 14.2 innings, he has produced a 3.07 ERA, 3.02 FIP, and 2.60 SIERA with a whopping 41% strikeout rate and a 20.2% swinging strike rate.

That performance has led Craig Counsell to deploy Jackson in more high-leverage outings this month. He has been called upon with a lead of five runs or fewer in seven of his nine September outings, once in a tie game, and once when down by one run. Jackson has responded by putting up a zero in seven of those appearances.

Obviously, we’re still dealing with a small sample size, and when Jackson does allow contact, it often results in damage. His expected wOBA on contact is .436, and his 11% barrel rate is below-average. He also needs to find a way to make his fastball more effective, as opponents are slugging .676 against it and have already smacked four home runs. That’s an issue that he’s going to have to resolve in order to carve out a successful big-league career.

While he’s somewhat of a journeyman at this point, it’s worth remembering that Jackson is essentially a rookie. His recent results indicate that he’s starting to become acclimated to facing MLB hitters. His slider looks legit, and he has put himself on the Brewers’ radar with his ability to generate swings and misses. If Milwaukee is going to secure a second consecutive playoff birth (and advance in postseason play), Jackson is going to play a role in it, and he could easily take hold of an important bullpen role next season. He’s a name to watch moving forward.

Statistics courtesy of Baseball-Reference, FanGraphs, Baseball Prospectus, and Baseball Savant.