Stacks are the backbone of cashing daily fantasy baseball lineups. Correlation drives upside, creating the potential to place high or even win GPPs when your selected stacks explode offensively.

This column will do the digging and the dirty work to determine which stacks are worth rostering each day. Scoring upside will fuel the stacks that get the nod. Sometimes that will lead to chalky selections, but contrarian stacks will get their fair share of love too.

In addition to utilizing the touted daily stacks in handbuilt lineups, numberFire premium members can throw these highlighted stacks into an optimized lineup using our DFS Sharpstack tool. Our hitting heat map tool is also available to premium members looking for more stacking options. It provides valuable info such as implied total, park factors, and stats for identifying the quality of the opposing pitcher.

Let's take a look at the top stacks on today's main slate.

Houston Astros

The Houston Astros are hands down Major League Baseball's best offense against lefties this season. According to FanGraphs, their 123 weighted runs created plus (wRC+) is eight points clear of the second-best offense against southpaws. So now, when I tell you the southpaw they're facing has a 1.29 ERA and 2.88 skill-interactive ERA (SIERA), you might think twice about stacking the 'Stros.

Not so fast. Nestor Cortes has earned his sterling ERA and SIERA almost entirely out of the bullpen this year. Cortes has pitched only six innings in three starts in his career, getting hammered for 13 runs (10 earned runs) on 13 hits, 2 homers, 3 walks, and 7 strikeouts. He's also yielded an eye-popping .497 weighted on-base average (wOBA) in his limited starts.

Perhaps Cortes's bullpen work this year is what he needed to turn the corner as a starter. Nonetheless, even if that's the case, the Astros can hammer even the best lefties, and I'm confident saying Cortes falls short of elite-lefty status. Carlos Correa ($3,800) is an excellent option. Kyle Tucker ($3,400) is a strong pick, too.

However, my favorite stacking options are Jose Altuve ($4,200), Yulieski Gurriel ($3,100), and Yordan Alvarez ($4,100). Altuve has a 140 wRC+ against lefties this year. Alvarez has been a pinch worse with a 137 wRC+. Gurriel has been the best of the bunch, ripping off a 164 wRC+. Additionally, Gurriel has a superb .250 isolated power (ISO).

San Francisco Giants

The San Francisco Giants are a nightly high-upside play with salaries that belies their ceiling. They're facing 34-year-old journeyman-righty Paolo Espino tonight. Espino's 2.48 ERA this year greatly overstates how well he's pitched, as evidenced by his 4.37 SIERA. He's a crafty, soft-tossing righty who relies on called strikes and rarely misses bats.

The prospect of stacking the powerful Giants lineup against him is tantalizing. Speaking of San Francisco's power, they lead Major League Baseball with a .195 ISO against righties in 2021. They also rank fourth in wRC+ (110) against righties. The Giants are capable of turning Espino into a pumpkin tonight and earnestly beginning the regression process for him.

You can take your pick stacking up and down the order. Although, my two favorite options are Mike Yastrzemski ($3,000) and Brandon Crawford ($3,100). Yastrzemski has smashed righties for a .309 ISO and 147 wRC+ in 2021. Crawford's fared even better with the platoon advantage, amassing a .377 on-base percentage, .280 ISO, and 156 wRC+.

Toronto Blue Jays

Shane McClanahan is a challenging matchup for the Toronto Blue Jays. The rookie lefty has faced them twice, holding them to one run in five innings the first time and three runs in 5 and 1/3 innings the second time. Perhaps the matchup coupled with 13 other games on the slate will keep the Blue Jays from being too chalky.

Their upside is through the roof. Toronto's lineup is stacked, and they rank tied for sixth with a 107 wRC+ against southpaws. So any opportunity to stack them without them being super chalky is appealing.

There's no shortage of stacking options in Toronto's deep, talented lineup. Whittling the picks down, though, Bo Bichette ($3,600), Vladimir Guerrero Jr. ($4,500), Teoscar Hernandez ($3,200), and Randal Grichuk ($3,500) represent Toronto's four most accomplished hitters against lefties this year. Grichuk's 143 wRC+ is the lowest of the quartet, and Hernandez's 173 wRC+ is tops. Bichette and Vladito are sandwiched between Grichuk and Hernandez with a 168 wRC+ and 171 wRC+, respectively. Marcus Semien ($3,900) also has a compelling case for usage with a .240 ISO and 131 wRC+ against lefties this season.

Joshua Shepardson is not a FanDuel employee. In addition to providing DFS gameplay advice, Joshua Shepardson also participates in DFS contests on FanDuel using his personal account, username bchad50. While the strategies and player selections recommended in his articles are his/her personal views, he/she may deploy different strategies and player selections when entering contests with his/her personal account. The views expressed in his/her articles are the author’s alone and do not necessarily reflect the views of FanDuel.