Just about anyone can recommend buying low on a star-caliber player with a lengthy track record whose early season stats simply aren't matching up with the back of his baseball card. But let's dig a little deeper, shall we?
We're far enough into the season now that some underlying numbers and metrics can no longer easily be brushed aside as "small sample size." In many cases, taking the time to peek under the hood can uncover underperforming players whose production hasn't synced up with their abilities … yet.
Here are four such names for your buy-low consideration.
Gregory Polanco, OF, Pirates
Polanco got off to a rather torrid start, totaling five long balls and 15 RBIs to go with a 1.099 OPS in his first 11 games. Since then? Try one homer, three RBIs and a .548 OPS. That's enough to frustrate any owner -- and open a window to target Polanco on the cheap.
Admittedly, the 26-year-old's raw potential always has tantalized, and that can be an easy trap to fall into. But there are signs that Polanco is adjusting as a hitter, even if the results haven't necessarily been there of late.
First, he's sporting a career-high walk rate (13.1 percent), an indication of improved patience and plate discipline. Second, there's the career-high ISO (.215), showing that latent power could be emerging. And third? His career-high average launch angle (21.6 degrees) is one of the 20 highest in baseball, according to Statcast™. Even with the increase in fly balls, Polanco's .224 BABIP is bound to come around, bringing up a .207 average.
The hope that Polanco might merge all of his tools and become the all-around fantasy star some projected when the former top prospect debuted in 2014? That might be unlikely at this stage, as he's yet to hit above .258 in any season and produced diminished stolen-base totals in each of the past two years (17 in 2016, eight in 2017) after tallying 27 steals in 2015. But a spike in power could mean Polanco approaches 30 home runs as he enters his prime seasons, and he's athletic enough to provide double-digit steals as a bonus.

Matt Carpenter, 1B/2B/3B, Cardinals
It has been a long first six weeks for the owner in your league who's had to endure Carpenter's .158 batting average. That's the second-lowest mark in baseball to teammate William Fowler's .155 (side note: what's going on in St. Louis?).
You probably don't even need to point that out as part of your pitch to deal for the versatile Cardinals veteran, but it can't hurt to note to his owner that this could signify the continuation of a downward trend for the 32-year-old Carpenter, who hit a career-worst .241 in 2017.
Here's why Carpenter still should be a catch, though: He continues to walk at an elite rate (a career-high 18.1 percent, in fact), and his .197 BABIP -- one of the 10 lowest in MLB -- is screaming for a correction.
On top of that, Carpenter has a .518 expected slugging percentage (xSLG) and .395 expected weighted on-base average (xwOBA) -- a pair of Statcast™ metrics that highlight a player's expected numbers based on his batted balls and plate discipline. Carpenter's negative-.211-point differential in SLG-xSLG and negative-.114-point gap in wOBA-xwOBA are both among the five largest in baseball. Put simply: Dude's been incredibly unlucky.
Go make a below-sticker price offer, then enjoy Carpenter's turnaround and always useful multi-position eligibility.
Marcus Stroman, SP, Blue Jays
Stroman had his breakout campaign a year ago, posting career bests in wins (13) and ERA (3.09). His encore so far has been disappointing, as he currently owns a 7.52 ERA and a 1.64 WHIP. That's the kind of start that will make any Stroman owner hesitant to start him until he works through any kinks and shows he's capable of not hurting the bottom line in those two pitching categories.
So why not jump in and suggest you take Stroman and his struggles to your roster? While not great, the 27-year-old's 4.40 FIP means he's been pitching better than the results show, and his 3.79 xFIP -- a metric that normalizes home run rate -- looks downright promising.
Stroman never has been a huge strikeout pitcher (7.3 K/9 entering 2018), but he is up to a career-high 8.4 through his first six starts. And he continues to rack up worm-burners, with a 60.8 percent ground-ball rate that is second-best in the sport (min. 30 IP).
Coming off two seasons of 200-plus innings, Stroman has shown he can be durable and effective when locked in. And even if it's just a hunch, the guess here is that a player known for carrying a chip on his shoulder with him to the mound is going to want to prove his slow start is just that. There's fantasy SP3 upside here, and he can be had at a streaming-starter price.

Max Kepler, OF, Twins
Kepler isn't a buy-low candidate because of especially subpar performance -- he's doing just fine with a .274 average, 14 runs, four home runs and 13 RBIs through his first 31 games. But nothing there jumps out at you and yells, "There's a star-caliber hitter waiting to break out here!" And so, Kepler remains something of an underappreciated player without much of a fantasy reputation, and thus an intriguing trade target.
At 25 years old and in only his second full big league season, Kepler -- once a top prospect -- has room for growth, and he's making progress. To wit, his 13-to-16 BB/K ratio (in his initial 126 plate appearances) is a drastic improvement over his career marks coming into 2018.
Kepler also is making adjustments against same-sided pitching. After struggling mightily to hit lefties early in his MLB career (.152/.213/.240 with 40 K's in 137 PAs from 2015-17), he is hitting .308/.379/.538 with only four strikeouts against lefties this year. Sure, it's only 29 plate appearances, but it's a start.
All of which is to say, there seems to be more in here. If it all clicks for Kepler, he could turn into a Christian Yelich-type hitter, but with more pop and less speed. That translates to an OF3 with the potential for more. It won't cost nearly that much to acquire him, though.