Champ or Chump: Trevor Story and Ronald Acuna Jr.

We begin our ridiculously early look at the 2019 fantasy baseball landscape with two of the bigger breakouts of the 2018 season. Trevor Story has gone from a barely top-100 asset to a potential MVP candidate, returning tremendous value to anyone who drafted him in March. Ronald Acuna Jr. should probably win the National League's Rookie of the Year award, likely earning some consideration as a fantasy MVP in the process.

Our question is simple: with both players likely to command high prices in redraft leagues next year, will they be worth it? They both have enticing tools, but Acuna may prove too raw to avoid a sophomore slump in 2019.

Let's take a closer look.

The Fantasy Jury is Out

Trevor Story (SS, COL) - 93% Owned

Story always offered the power-speed blend that fantasy owners crave at the expense of batting average. This year however, he's managed a .291/.346/.555 line with 33 HR and 26 SB (six CS). As Colorado's regular cleanup hitter, he's been a true five category stud in 2018.

Both the speed and power should be sustainable. Lost in his prestigious power is plus-plus speed. His 29.6 ft./sec Statcast Sprint Speed ranks 15th in all of MLB, ahead of several burners such as Manuel Margot, Amed Rosario, and Rajai Davis. His 81% success rate on the bases is also excellent, ensuring that the Rockies give him the green light to shoot for 30 bags next year.

While his 19.1% HR/FB may seem high, Story's career rate is 19.3%. His average airborne exit velocity (94.7mph) and rate of Brls/BBE (12.2%) are more in line with his exciting 2016 (94.9mph, 13.9%) than his disappointing 2017 (93.8mph, 10.5%), giving him well above average contact quality in two of his three big league campaigns. He also hits plenty of fly balls (43.2% FB%, 45.5% career) with a high Pull% (29.5% on flies this year, 26.4% career), taking full advantage of his extremely hitter-friendly home park (113 HR factor in 2017). Story is as safe a bet as any for 30 bombs in 2019.

Thus, Story's batting average will determine if he is a first-round fantasy talent or not. His plate discipline has historically been awful (8% BB%, 30.4% K%), but he has cut both rates in 2018 (6.9% BB%, 26.2% K%). Better yet, his peripherals support the reduced strikeout rate. His career 12.7% SwStr% is down to 11.4% this year, and he has been more aggressive than he has been in the past (50.4% Swing%). This allows him to end most PAs before he has an opportunity to strikeout, a clear benefit in fantasy since he hasn't compromised his contact quality to do it.

His .348 BABIP might look unsustainable, but his career rate is .343. He combines his plus wheels with above average exit velocity on ground balls (86.9mph), giving his grounders a high expected value even if a .333 BABIP is a little much. Contrary to what you might think, Story is shift-proof (.392 in 105 PAs this year) because he rarely pulls grounders (58.7% Pull%). Coors Field also inflates singles (111 park factor), doubles (112), and triples (128) for right-handed hitters, making it easier to maintain an otherwise unsustainable BABIP.

Some owners may discount Story because his BABIP and HR/FB are partially the result of playing at altitude, but there is no reason to expect that he's leaving Coors anytime soon. Story is a fantasy stud as long as your league doesn't regress a player's stats based on their home park.

Verdict: Champ

Ronald Acuna Jr. (OF, ATL) - 91% Owned

It wasn't always fun for fantasy owners to deal with Atlanta's service time shenanigans and then Acuna's efforts to play hurt, but his current line of .292/.368/.574 with 25 HR and 14 SB (five CS) makes up for it. There is a ton of upside in his profile, but also several red flags that suggest a sophomore slump might be incoming.

Let's begin with his .343 BABIP. One reason for his mark to date is a .313 BABIP on grounders--probably too high to count on moving forward. Sure, he runs as fast as Story (29.6 ft./sec Statcast Sprint). Yes, his average exit velocity on ground balls is slightly higher than Story's (87.2mph). However, he plays in a neutral park for BABIP and may have an issue with the shift in the future.

To be clear, Acuna hasn't minded the shift in 2018 (.366 in 124 PAs against the shift, .326 in 130 without it). However, his 67.8% Pull% on ground balls is right on the cusp of the danger zone. If it increases by even a few percentage points in 2019, Acuna's BABIP on grounders could free fall.

Acuna's advocates are likely to cite his MiLB track record as evidence that he can sustain elevated BABIPs, and he certainly had a hell of a season in 2017. It started in Double-A Mississippi, where he slashed .326/.374/.520 with nine homers and 19 SB (11 CS) in 243 PAs. He was then promoted to Triple-A Gwinnett, where he slashed .344/.393/.548 with nine homers and 11 swipes (six CS) over another 243 PAs. His BABIP at Double-A was .396, and his mark at Triple-A was .404.

The problem is how he put up those marks. In Double-A, Acuna posted a LD% of 25.2%. At Triple-A, it actually increased to 26%. The rest of Acuna's track record is devoid of such elevated marks, and it actually collapsed to just 12.3% in his 101 Triple-A PAs this year. Likewise, his major league LD% of 18.3% is significantly below league average. There is no evidence that Acuna has a distinct line drive swing, calling the validity of his 2017 BABIPs into question.

Acuna's 40.3% FB% also exerts downward pressure on his BABIP, but it's responsible for his significant power potential. His 95.2mph average airborne exit velocity ranks 60th in baseball this year, while his 14.3% rate of Brls/BBE ranks 14th. Taken together, these two stats suggest that his contact quality is excellent, in turn supporting his 22.3% HR/FB.

Incidentally, Acuna's HR/FB wasn't that high on the farm. He posted a HR/FB of 15.3% at Double-A Mississippi last year, but that's actually well above average when the stadium's HR factor is considered (0.554 from 2014-2016).  Likewise, his 17.6% HR/FB at Triple-A Gwinnett looks much better when the ballpark's 0.885 HR factor is considered. While Acuna's batting average could regress in 2019, his power should prove sustainable.

Unfortunately, the same cannot be said for his steals. Acuna has foot speed, but his 73% success rate on the bases leaves little room for error if he hopes to have a green light. He was even worse in the minors last year, posting a 63% success rate at Double-A and 65% at Triple-A. The Braves also view Acuna as a generational player (and rightfully so), so they might slow his running game so that he can stay in the lineup and hit dingers.

Acuna has a good approach at the plate (9.7% BB%, 24.5% K%) backed by peripherals (28.2% chase, 11.4% SwStr%), so his floor is definitely higher than the average 21-year old in the major leagues next year. His power should show up, but his average could fall to the .270-.280 range while his steals dry up. That's still a fantasy asset, but the hype might make him a first-rounder next year. You need more in the first round in redraft leagues.

Verdict: Chump (in the 1st round)