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.

Los Angeles Angels

The Los Angeles Angels have been off for two straight days after their games on Saturday and Sunday were postponed due to members of the Minnesota Twins testing positive for COVID-19. They'll come out of their two-game break as my favorite stack in a plus matchup.

Kohei Arihara has walked a tight rope with a pitch-to-contact approach in three starts, recording a 3.07 ERA. Speaking to his pitch-to-contact approach, he's struck out only 12.3 percent of the batters he's faced with, according to FanGraphs, a 7.4 swinging-strike percentage. He's been fortunate on his batted balls, though, as evidenced by his 4.67 skill-interactive ERA (SIERA) and his .323 weighted on-base average (wOBA) that's 82 points lower than his .408 expected weighted on-base average (xwOBA), per Baseball Savant.

Regression is around the corner. I expect the Angels to begin that process in earnest tonight.

David Fletcher ($3,100) is an adequate stacking option from the leadoff spot. Justin Upton ($3,000) has the thump to punish Arihara's contact-heavy approach, sporting a .214 isolated power (ISO) against righties since 2018. He's a usable option, too. However, it's a trio of hitters I'm locked in on.

Shohei Ohtani ($4,400), Mike Trout ($4,600), and Jared Walsh ($3,500) are must-use options in an Angels stack. The two-way star, Ohtani, has been a man on fire in 2021, rattling off four homers, two stolen bases, a .370 on-base percentage, .373 ISO, and 198 weighted runs created plus (wRC+).

Trout's an annual MVP favorite, and he's lit righties on fire with a .447 on-base percentage, .363 ISO, and 192 wRC+ in 1,098 plate appearances against them since 2018. Walsh hit at every level of the minors, and after struggling in his initial call-up in 2019, began to make the transition to the bigs last year. In 106 plate appearances against righties since last year, he's amassed a .377 on-base percentage, .452 ISO, and 199 wRC+.

San Francisco Giants

I technically wasn't lying above when I called the Angels my favorite stack. They are, but so are the San Francisco Giants. The beauty of these teams being my co-favorite stacks is the integral pieces from both coexist well on the same roster.

Chase Anderson has the highest SIERA out of tonight's probable starters at a robust 5.64. He also has the highest homers per nine innings at 2.00. Toss in Anderson's .362 xwOBA and the third-highest park factor for homers (1.202) in Major League Baseball at Citizens Bank Park, per FantasyPros, and I'm completely enamored with the Giants tonight.

Tommy La Stella ($2,200) is a usable punt in this stack, leading off for the Giants. Mike Yastrzemski ($3,000) is a marvelous selection from the two-hole with a .251 ISO and 125 wRC+ against righties since 2018. Platoon outfielder Alex Dickerson ($2,300) belongs in the stacking conversation, too, with a .244 ISO and 129 wRC+ against righties since 2018. Although, Dickerson is a probable candidate to be lifted early for a pinch-hitter, pinch-runner, or defensive replacement late.

My three favorite stacking options from the Giants, in order, however, are Evan Longoria ($3,100), Brandon Belt ($2,300), and Brandon Crawford ($2,600). Longoria's a Statcast darling this year, ranking tied with J.D. Martinez, Willson Contreras, and teammate Crawford for 15th out of 216 hitters with a minimum of 25 batted-ball events in barrels per plate appearance percentage, according to Baseball Savant. He also ranks fifth in fly-ball/line-drive exit velocity at 101.5 miles per hour. Further, as a right-handed hitter, he'll be treated to Anderson's .548 slugging and .373 wOBA coughed up to 101 right-handed batters since 2020.

Belt has terrorized righties on the road throughout his career, including in recent years. Crawford's often lauded for his glovework, but he can put a charge into the ball, too. The trio of Longoria, Belt, and Crawford can be stacked with Ohtani, Trout, and Walsh while leaving ample salary-cap space to roster one of the top pitching options and fill out the remaining hitter slots.

Kansas City Royals

For full disclosure, I'd rather sprinkle a few of the Kansas City Royals around the Angels and Giants, but they have their own compelling case for stacking in a plus matchup. Opposing starter Josh Fleming's 5.09 SIERA is the second-highest mark among today's probable starting pitchers. He also takes a more pitch-to-contact approach than Arihara, with a paltry 9.5 strikeout percentage. The lefty does a poor job filling up the strike zone, too, with a 9.5 walk percentage. It's not hard to envision him putting plenty of traffic on the basepaths and getting punished for it.

Out of yesterday's lineup against lefty Robbie Ray, only Kyle Isbel ($2,200) and Nicky Lopez ($2,200) are completely unappealing. My favorite picks are Hanser Alberto ($2,100), Jorge Soler ($2,700), Carlos Santana ($2,600), and Whit Merrifield ($3,900). Using the quartet together is the best stack of the Royals.

I also love Merrifield as a one-off option. In 482 plate appearances against lefties since 2018, he has a .367 OBP, .195 ISO, and 133 wRC+. I'd also be doing Merrifield an injustice if I didn't mention his elite base-stealing prowess. He's stolen five bases in six attempts this year, and he swiped a dozen in 15 attempts last year. He's a great piece of exposure to the Royals tacked onto an Angels and Giants two-some.