For this week's iteration of Statcast Studs and Duds, it's back to the expected stats. This time, we'll look at slugging percentage by comparing players' Expected Slugging (xSLG) to their actual Slugging (SLG) rates.

For those unfamiliar with this metric, Expected Slugging Percentage (xSLG) is formulated using exit velocity, launch angle and, on certain types of batted balls, Sprint Speed. Statcast attempts to measure what the most likely outcome would be for each batted ball in order to evaluate a player's skill, regardless of outcomes.

Now, let's examine the top and bottom of the xSLG-SLG leaderboard to find buy/sell/add/drop candidates for 2019 fantasy baseball leagues as we head to the start of summer.

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Overachieving Sluggers

All stats current as of May 27, 2019 and display leaders among hitters with at least 100 plate appearances (PA).

.166 xSLG-SLG in 154 PA

Renfroe has lived up to late-round fantasy sleeper status this season with 14 home runs and 29 RBI after two months of play. He is slowly making his way into fantasy lineups, so it is important to know that he is second on the list of hitters who are performing far higher than Statcast expects them to. Renfroe's .611 SLG would be good for ninth if he had a few more AB to qualify for the batting title. His expected numbers are far lower though and fall right in line with his xSLG from the past two seasons.

Pitchers are adjusting to Renfroe this year now that he's a mainstay in the lineup. He's seen a four percent swing away from fastballs toward more breaking stuff, which he struggles mightily against. His .705 SLG against fastballs is scary but his .408 SLG against breaking balls is pedestrian. Teams are also shifting him much more than before. He is seeing a shift 68.8% of the time compared to 27.6% last year and it's resulted in a -.162 difference in wOBA. Renfroe will still turn on the occasional fastball and produce 25-30 HR this year but it will be sporadic and come at the expense of average. Renfroe is best used in 14+ team leagues or as a DFS play against pitchers with an aggressive approach.

.138 xSLG-SLG in 146 PA

We knew Tapia wasn't going to bring much thunder - he's never hit for power and probably never will much. The fact he even has five homers so far is surprising. His high for a season is 12, back in Single-A Advanced in 2015. His .369 xSLG is somewhat low so it's not as if he should crash and burn but Tapia just isn't a power hitter and the Coors factor doesn't change that.

Tapia's main value lies in points leagues. His four triples and nine doubles do fantasy owners more favors there and explain part of his elevated slugging percentage. His 23.3% K-BB% is alarmingly high for a contact hitter who won't flex much power so there's cause for concern there too but he is still performing like a solid OF4 with upside for more. As long as he stays at the leadoff spot of the Rockies lineup, he is a fantasy asset. If he drops lower in the order, he may need to hit the bench in roto leagues.

.122 xSLG-SLG in 164 PA

We continue our sweep of NL West outfielders with a look at one of the top home run hitters of the first two months. Pederson owns a .616 slugging percentage that ranks eighth among qualifiers and is tied for 10th in the bigs with 14 HR. He has always had power so it's not a shock that he's performing this way while maintaining a .252 average. His exit velocity is in the 90th percentile and hard-hit rate in the 83rd percentile, while his .406 wOBA is in the top seven percent of the league. Everything seems to check out. Except it doesn't.

His absurd .370 ISO and inflated 31.1% HR/FB are definitely unsustainable, as they are both far above his career norms. The other thing is that much of his damage was done in the very first week of the season. His xSLG is still above the Major League average, but not significantly.

Most fantasy owners recognize that Pederson wasn't going to keep up his April production, which he hasn't, so there isn't much opportunity to sell high if there ever was. Pederson can certainly reach the 30-homer mark for the first time in his career but he's also never reached 70 RBI and doesn't seem likely to do so with 27 RBI after two months that most likely included his most prodigious power output. Pick your spots with Pederson and temper expectations - he is what he is at this point.

Underachieving Sluggers

All stats current as of May 27, 2019 and display leaders among hitters with at least 100 plate appearances (PA).

-.197 xSLG-SLG in 158 PA

Three weeks ago, I identified Morales as an xBA underachiever, along with Aguilar (below). After he was DFA'd by Oakland, it looked as if Morales might lose all fantasy relevance for this season. Then he was picked up by the Yankees, who are happy to just have a warm body on their roster that isn't hurt. Morales couldn't have landed in a better spot, as Yankee Stadium is number one in HR Factor by handedness for left-handed batters. The switch-hitting Morales will see most of his at-bats from the left side as he fills in at first base and allows Luke Voit to be an everyday DH.

He's currently hitting .196 after an 0-for-5 day at the plate which may be hard for fantasy owners to stomach. He isn't going to hit north of .250, which he hasn't done since 2016, so just accept that you're buying him for power only. There is some hope though, as his team context is good and could get much better if Aaron Judge comes back soon; I've given up on Giancarlo Stanton. Morales isn't just the leader in negative differential for xSLG-SLG, it's by a wide margin over the next closest player. If his playing time persists and his luck turns around, Morales could be a cheap source of power.

-.128 xSLG-SLG in 158 PA

The Smoak Monster made his presence known on Memorial weekend, going deep twice on Sunday afternoon against the Padres. That makes 11 HR for Smoak in a "disappointing" start to the season. His power numbers are just fine, as he's now on pace to approach his career-year numbers from 2017. The big difference is the batting average, which was at .219 before Sunday and was showing a downward trend after he hit .242 last year. Now we know that he's really underperforming based on the .553 xSLG that ranks 22nd among all qualified batters. His .280 xBA places him fourth among xBA-BA differential leaders, so his average is bound to jump up along with his power.

It should also be noted that he has improved his walk rate to an outstanding 17.9% that's almost even with his 19.4% K%, both of which are career bests. Smoak has been largely forgotten after last year because everyone assumed 2017 was an outlier. It turns out he could be a great buy-low before positive regression hits.

-.108 xSLG-SLG in 158 PA

If you're an Aguilar owner, it probably isn't much consolation to know that he should be doing much better than he is. The big man had an awful April, lost playing time, and was dropped in many leagues. Then it looked like he was turning a corner when he jacked three HR in a two-day period to end April. He hasn't gone deep since, making him homerless for the month of May. It's astounding how someone who posted a .264 ISO in 2018 and a .240 ISO in 2017 could drop all the way to a .102 ISO this season with a slugging percentage of just .299.

His exit velocity is nearly the same as last season and there are no extenuating circumstances to explain his huge decline, as he's in the same park, position, lineup spot, etc. So what's the issue? Timing, pure and simple. Aguilar isn't getting around on fastballs, posting a .212 xBA on heaters compared to a .300 xBA last year that resulted in a .332 average against the fastball. You can see below that his xSLG remains the same on offspeed pitches and has actually gone up on breaking pitches.

While we still don't know the root cause, we must hold out hope that Aguilar gets his mojo back at some point. He doesn't need to be in lineups anywhere until he starts leaving the yard but it might be wise to keep him stashed on the chance he catches fire.