xSLG isn’t a stat you’ll find on the back of a baseball card or one you’d find on a baseball reference page. However, as far as advanced stats go, xSLG is pretty straightforward. It is the expected slugging percentage of a hitter based on hit probability his batted balls in play, regardless of outcome. So if a player has a high xSLG but low SLG, he’s probably experienced some bad luck on batted balls. Likewise, if a player has a high SLG but low xSLG he’s probably been a little fortunate in the power department.

In this article we’re going to look at some of the leaders in xSLG from the 2018 season, and break down whether their 2018 production is sustainable and look ahead to their 2019 value. For this article, the known quantities were omitted. We know players like J.D. Martinez (.620 xSLG in 2018) and Mike Trout (.589 xSLG) are great hitters, so instead we’ll focus on players with more uncertainty going into 2019 - players that either broke out or underperformed in 2018.

These players all carry some degree of doubt or questioning heading into 2019, so we’ll be breaking down their batted ball profile in terms of xSLG and contextualizing their value based on NFBC ADP (as of 01/06/19).

Notable Expected Slugging Leaders from 2018

Christian Yelich – OF, Milwaukee Brewers

2018 xSLG: .554 (rank: sixth)

Plenty of league champions had Christian Yelich on their team last season, especially those in weekly leagues, since Yelich came up big down the stretch. He was playing well in the first half, posting a .292 AVG, .823 OPS, and .167 ISO, but those were just typical Christian Yelich numbers. Yelich transformed into a full-blown superstar in the second half, posting a .367 AVG, 1.219 OPS, and .402 ISO. His 25 second half home runs would’ve been a career high even if he hit zero in the first half.  Anyone that’s followed Yelich’s career path with the Marlins knew there was dormant power potential inside him. He has always pulverized the ball, with a career 91.6 MPH average exit velocity. His 92.3 MPH average exit velocity last season wasn’t even a career high; he slightly edged it out in 2016, yet his .554 xSLG was a career high by 57 points. So why now? What was different about 2018 that allowed Yelich to finally have the power breakout?

For starters, a one-way ticket out of Miami helped. As a Marlin Yelich had a .118 career ISO in Miami, compared to a .163 ISO on the road. Marlins Park is known to favor pitchers, and with Yelich’s groundball-heavy approach he didn’t have a prayer of posting elite power numbers while calling Marlins Park home. Speaking of groundballs, Yelich has slowly been decreasing his groundball rate year after year. He had a 63.2% groundball rate as a rookie but had a 51.8% groundball rate last season. It probably won’t drop any farther, but that is a big improvement in terms of power. The lack of flyballs kept his home run total low in the past, but Yelich got pretty fortunate on the flyballs he did hit last year. He posted an insane 35% HR/FB ratio. Since 2002, the first year the statistic was tracked, only three qualified batters have ever had a HR/FB ratio of 35% or higher. Ryan Howard in 2006, Aaron Judge in 2017, and Christian Yelich in 2018. Both Howard and Judge hit over 50 home runs in their miracle seasons, but Yelich only hit 36 in 2018.

The improvement Yelich made are fantastic to see. He made legitimate strides by hitting more line drives and fewer groundballs, posting a career-high 12.9% barrel rate, and putting up top-5% numbers in every StatCast expected statistic. However, it is likely that we saw Christian Yelich’s best season last year, and it’s often unwise to pay full price for a career year. He’s a first-round pick in all leagues, but be wary of spending a top-five pick on Yelich this draft season.

Shohei Ohtani – DH, Los Angeles Angels of Anaheim

2018 xSLG: .539 (rank: eighth)

Who knew the Japanese phenom with a 100-MPH fastball and deadly splitter could hit? Not many people expected the two-way superstar to be this effective with the bat, but Ohtani put up a .925 OPS, .279 ISO, and 22 home runs in 367 PA last season. He’s already undergone Tommy John surgery and won’t pitch in 2019, but he could serve as the Angels’ designated hitter during his rehab. We don’t know whether that will be full-time or part-time or at all, since rehab from Tommy John can be grueling and the Angels should be focused on getting him fully recovered, but the opportunity is there for Ohtani to play regularly.

If Ohtani were to spend time as a DH the underlying numbers are juicy. He not only posted the eighth-best xSLG of 2018, but had the 11th-highest average exit velocity and the sixth-highest barrel rate. When Ohtani makes contact, he hits the ball well. Making contact was a bit of a problem for him, however, as he had a mediocre 71.6% contact rate and a 27.8% strikeout rate. Players in today’s game can get away with this, but it’s certainly a red flag against him. Despite the immense talent Ohtani was a rookie last season and had never seen MLB-quality pitching before, so there is plenty of room for growth for the 24-year-old. If Ohtani gets full-time plate appearances next season he could hit 30 home runs with a solid batting average. His .285 mark from 2018 seems a little high, especially given his .350 BABIP and poor contact rate, but .275 seems realistic. He is currently going 101 in NFBC ADP, which is a pretty risky pick considering one could draft Travis Shaw at 102 or get Max Muncy at 97 instead. Still, if the Angels bench or cut Albert Pujols and let Ohtani play every day he could be a value at 101.

Kendrys Morales – DH, Toronto Blue Jays

2018 xSLG: .537 (rank: 12th)

Most fantasy owners don’t care about boring old veterans like Kendrys Morales. He just blocks exciting players, like Vladimir Guerrero Jr., Bo Bichette, Cavan Biggio, and Rowdy Tellez from the majors. Last year he clogged up the DH spot, indirectly causing Josh Donaldson to aggravate his shoulder injury because Donaldson had to play third base. He just isn’t worth anything to us. That’s evident in his ADP, as Morales is going at pick 476. He’s even being drafted behind Rowdy Tellez, despite Morales having the inside track over Tellez. He’s also going behind the likes of Alex Gordon, Hunter Dozier, Freddy Galvis, Yolmer Sanchez…you get the picture. He’s an afterthought in fantasy baseball, which is why it’s surprising to see Morales rank so highly on the xSLG leaderboards.

Not only does Morales excel in xSLG, he shines in pretty much every Statcast hitting category. He has a .537 xSLG compared to a .438 SLG, a .384 xwOBA compared to a .329 wOBA, and a .282 xBA compared to a .249 BA. He also had a 92.3 MPH average exit velocity last season along with a 52.6% hard-hit rate. So why did he finish with a slightly above average 108 wRC+ last year? Other than his seven-homer streak in August Morales barely seems to have done anything in 2018. Before we get all excited about Morales as a deep sleeper next year, consider that he has routinely put up elite StatCast numbers since it was first implemented in 2015. The 2015 season would also be his closest thing to a monster year, where Morales had a 131 wRC+. After three straight years of elite StatCast numbers but merely passable actual numbers, his underperformance can’t be considered a fluke.

One problem for Morales is groundballs. His 10-degree average launch angle and 45.8% groundball rate would be fine for most players, but for Morales groundballs are especially bad. It doesn’t take StatCast to tell us a 35-year-old DH with screws in his knee is slow, but in case you were wondering Morales ranked 541 out of 549 players in sprint speed last season. Furthermore, he had a .176 BABIP and -11 wRC+ on groundballs last season compared to a league average .236 BABIP and 30 wRC+. Groundballs have been demonized perhaps too harshly in the modern game thanks to teams emphasizing launch angle, but in Morales’ case, the grounders have to go. He was above average on fly balls and line drives last season, and could be a much better hitter if he raises his launch angle. He’s a decent late-round flyer since Morales is on nobody’s radar, but don’t be afraid to abandon ship quickly. It would be nice to see a team like the Astros or Rays take a chance on Morales for cheap via trade, but that seems unlikely given how both teams’ off-seasons have played out.

Max Muncy – 1B/2B/3B, Los Angeles Dodgers

2018 xSLG: .535 (rank: 13th)

Muncy came out of nowhere to be one of 2018’s biggest surprises. The 28-year-old Oakland burnout didn’t even make the Dodgers’ opening day roster, but after being called up in mid-April Muncy forced himself into the lineup, and finished with a .973 OPS and 35 home runs on the year. It’s nice to see Muncy rank highly on the xSLG leaderboards, because whenever a player emerges from nothing, as Muncy did, underlying statistics like xSLG play a huge role in determining their sustainability.

As a prospect, Muncy wasn’t much of a power hitter. The .319 ISO he had last season was by far his highest mark as a professional. The only other time he had an ISO above .200 was at High-A ball in 2013. Muncy’s increase in power came from a theoretically simple change; swing harder.  He increased his hard-hit rate from 32.3% in 245 PA with Oakland to 47.4% in 481 PA with the Dodgers. His 90.3 MPH average exit velocity was 7 MPH higher than his last stint in the majors in 2016. He paid for it with strikeouts too, with a meager 72.9% contact rate and 80.4% zone-contact rate last season. His 27.2% strikeout rate was much higher than the mid-teens strikeout rates he typically had in the minors. But if that’s what it costs for elite production at the plate, then so be it. His 16.4% walk rate helps offset the damage of strikeouts in points leagues as well.

Other than track record, Muncy only has one glaring red flag, but it’s a big one. His 29.4% HR/FB was the third highest in 2018 (min. 250 PA). Since 2000 only two players have had back to back years with a 29% HR/FB or higher. One of them was Aaron Judge between 2017-2018, and the other was Ryan Howard, who did it three straight times from 2006-2008. Muncy’s HR/FB will almost certainly drop next season, and his power numbers and counting stats will fall with it. Even factoring that regression in, Muncy is a solid value at pick 97. He’ll have triple eligibility in some leagues, and his eye at the plate gives him a decent floor if power regresses.

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