Stacking is an integral part of daily fantasy baseball. Correlation drives upside, giving your lineups a slate-winning ceiling when your stacks explode.

This piece will do the digging and the dirty work each day to determine which stacks are worth rostering on FanDuel's main slate. While we want upside, we also need to factor in game theory, especially in a sport as random as baseball.

The MLB DFS heat map at numberFire is a quick way to get a feel for the overall slate and which offenses are in a good spot. You can also check out our daily fantasy baseball projections -- which are powered by numberFire -- to identify the slate's best bats.

Let's look at the top stacks for today's main slate.

MLB DFS Stacks

Pittsburgh Pirates

Implied Total: 5.20 | Opposing Pitcher: Ryan Feltner (R)

Rarely am I actively looking to stack the Pittsburgh Pirates, but they're in a nice spot to poor on runs at Coors Field. With Ryan Feltner on the bump for the Colorado Rockies, Pittsburgh has the slate's second highest implied total (5.20).

Through 13 starts, Feltner owns a 5.74 ERA and 1.48 WHIP. His ERA indicators -- 3.69 xERA, 4.02 xFIP, and 4.10 SIERA -- are fairly sound even though he suffers from pitching half his games at Coors Field. Away from Coors, Feltner has a 4.87 ERA and .333 wOBA against. At home, his ERA (7.30) and wOBA against (.373) both skyrocket.

This will be the second time Feltner has faced the Pirates this season after the Buccos smashed him for five runs across 5 2/3 innings in early May.

That outburst was highlighted by an Oneil Cruz's ($3,600) two-run home run, and he's who I'm starting any Pirates stack with. Cruz has had an up-and-down season, but he's consistently mashed right-handed pitchers. In that split, the lefty has a .368 wOBA and .214 ISO. Seven of his nine home runs have come against lefties, and he has the game's lowest odds to hit a home run at +350.

But, Cruz isn't the highest-salaried Pirate tonight; that title belongs to Nick Gonzales ($3,700). Gonzales has been a model of consistency with hits in 17 of his last 20 games. He has a .343 wOBA against righties and leads Pittsburgh with 23 RBI since his May 10th call-up.

Cruz and Gonzales are my priorities in this stack, but Bryan Reynolds ($3,600) and Connor Joe ($3,500) are next in line. Among Pirates, Reynolds is third in wOBA (.323) and OPS (.733) against right-handed pitchers. Joe ranks fourth in wOBA (.312) but has an enticing 41.7% fly-ball rate in this split.

Andrew McCutchen ($3,400) and Ke'Bryan Hayes ($3,300) benefit from batting first and fifth in the Pittsburgh lineup. I'm more interested in McCutchen between the two. He has a serviceable .308 wOBA against righties is pacing the team in home runs (4) and runs scored (17) over the last month. We project McCutchen for 14.6 FanDuel points tonight, second among Pirates and good for the fifth-best point-per-dollar value on the slate (4.29 FanDuel points per $1,000).

With Feltner giving up a .375 wOBA to lefties (compared to .317 to righties), Jack Suwinski ($3,200), Yasmani Grandal ($2,900), and Rowdy Tellez ($2,900) are all in play as salary-savers. Tellez has the highest wOBA (.274) against righties, and he's notably belted four doubles in nine career plate appearances against Ryan Felter. But, Grandal (.143) and Suwinski (.126) have higher ISOs in this split.

Arizona Diamondbacks

Implied Total: 5.06 | Opposing Pitcher: Chris Flexen (R)

The Arizona Diamondbacks are the only team that has an implied total over 5.0 without the Coors Field bump. Though, facing the Chicago White Sox offers a similar advantage.

Chicago's south siders trot Chris Flexen out onto the bump tonight. Flexen has been positively dreadful through 12 starts, pitching to a 5.06 ERA and 1.30 WHIP. His fly-ball rate has ballooned to 47.4% this season, and that's played a role in him allowing a 1.27 HR/9. Consequently, Flexen's ERA indicators -- 4.41 xERA, 4.76 xFIP, and 4.70 SIERA -- are predictably shaky.

It doesn't hurt that White Sox relievers have allowed the league's second-highest batting average (.256) and sport the fifth-highest SIERA (4.09).

It's a mouth-watering matchup all around for Arizona, and that starts with the scorching-hot Christian Walker ($3,400). Walker has homered three times in the last two days, including a two-home run effort last night that netted 44.4 FanDuel points. He's shredded righties to the tune of a .366 wOBA and .245 ISO this season while Walker's 49.3% fly-ball rate has resulted in 12 of his 15 yabos coming in this split. He's tied for the shortest odds to hit a home run (+360) Diamondbacks.

Of course, it'd be hard to stack D-backs without Ketel Marte ($3,700). The switch-hitter hasn't been great against righties (.300 wOBA; .120 ISO), but he still leads Arizona with 11.9 FanDuel points per game on the year. Marte is also our highest-projected player, pegging him for 14.8 expected FanDuel points.

Corbin Carroll ($3,200) and Joc Pederson ($3,100) are my favorite upside plays here. Carroll's season-long numbers are still rough, but he's slowly started to figure it out over the last month, and he leads Arizona with 19 runs over that span. Pederson continues to be one of the top platoon bats in the game. He has a .378 wOBA and .865 OPS against right-handed pitchers for the year. Plus, he's coming off a 2-for-4 effort that saw him homer, drive in five, and score 41.9 FanDuel points.

Lourdes Gurriel ($3,200) and Eugenio Suarez ($2,800) are both pretty uninspiring at salary, and neither have a wOBA north of .270 against righties.

I'd rather dip down to Gabriel Moreno ($2,700) or Jake McCarthy ($2,700) to save salary and get better production. Moreno has a .322 wOBA against righties, while McCarthy is at .314. McCarthy could be a factor on the basepaths, too. His nine steals ranks second on the team while the White Sox have allowed the third-most steals per game (0.99) this season.

Whoever starts between Kevin Newman ($2,500) and Geraldo Perdomo ($2,400) would be a decent salary-saver, too. Newman has three hits in consecutive games and is hitting .270 against righties for the year. Perdomo has only appeared in nine games this season, but he posted a .328 wOBA against righties in 2023.

San Francisco Giants

Implied Total: 4.20 | Opposing Pitcher: Tyler Anderson (L)

Though the San Francisco Giants have a modest implied total (4.20), they're an under-the-radar stack that won't set you back much. In fact, only one hitter is salaried north of $3K in their matchup with the Los Angeles Angels.

The Angels are starting lefty Tyler Anderson, and he's the primary reason we can consider them as a value stack. Anderson's been rock-solid at face value, pitching to a 2.63 ERA with a 1.15 WHIP. But there's smoke under the hood -- first and foremost via a 45.3% fly-ball rate and 9.8% barrel rate.

Anderson's .218 BABIP and 86.6% strand rate and significantly better than his career marks, while his swinging-strike rate (11.6%) is down from 2023. With ugly ERA indicators -- 4.66 xERA, 5.02 xFIP, and 5.12 SIERA -- Anderson appears primed for a blow-up sooner or later.

San Fran could be the cause of that considering how well they've shredded lefties this season. They rank eighth in wOBA (.327) and seventh in wRC+ (117) against southpaws, and that's thanks in no small part to the scorching-hot Heliot Ramos ($3,600).

Ramos' third try at the MLB level appears to be the charm. He's hit .305 with a staggering 16.5% barrel rate since his early May call-up, and he's really taken off this month. Over an 11-game stretch, Ramos is batting .349 with four home runs and 11 RBI. He's posted a .359 wOBA and .259 ISO in 101 career plate appearances against lefties, making this the clear split to target him.

After Ramos, we have our pick of the sub-$3K litter. I want at least one of Matt Chapman ($2,900) or Jorge Soler ($2,700) given their stellar left-handed splits. Chapman has a .437 wOBA and 1.026 OPS against southpaws this season, and Soler isn't far behind via his .350 wOBA. We're just a year removed from Soler belting 14 homers in 135 plate appearances against lefties, culminating in a .442 wOBA and .411 ISO. He has the shortest odds to hit a home run (+340) in this game.

Michael Conforto ($2,900) has struggled lately, but his .360 wOBA against lefties is still manageable tonight.

I'll pass on Thairo Estrada ($2,800) and Patrick Bailey ($2,800) considering you can get Soler at a lower salary, but Austin Slater ($2,300) at least deserves a mention given his bottom-of-the-barrel salary. His left-handed splits aren't great, but he's leading off against lefties and is coming off a 25.2-FanDuel-point game.

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The above author is a FanDuel employee and is not eligible to compete in public daily fantasy contests or place sports betting wagers on FanDuel. The advice provided by the author does not necessarily represent the views of FanDuel. Taking the author's advice will not guarantee a successful outcome. You should use your own judgment when participating in daily fantasy contests or placing sports wagers.