Stacking is the most talked-about best-ball concept and one of the least-understood. Take a QB and one of his pass-catchers on the same fantasy team. In theory this doubles your ceiling on the week that QB throws for 400 yards and 4 TDs. In practice it depends on format, roster construction, and whether you are chasing spike weeks or a stable season.
The math, quickly
A standard QB touchdown pass is worth 4 points to the QB and 6 to the receiver (plus PPR + receiving yards). So one 40-yard TD from Josh Allen to a WR you also rostered scores you:
Without the stack, if that WR were on someone else's team, you get 5.6. The stack roughly triples the ceiling of the play. Now multiply across a full 4-TD game and you can see why stacking wins tournaments.
When stacking is a good idea
Best ball, especially tournaments. The ceiling matters. Correlation compounds.
SFB and TEP formats. TE premium formats magnify the stack multiplier when the TE is the target.
High-total games. If Vegas has a game at 51+, both offenses are more likely to feed skill guys. Game stack (a WR from each team) is even better than a single-team stack in those spots.
When you already like the QB. Never force it. If the QB is not on your board, do not draft an inferior QB just to stack.
When stacking is a bad idea
Head-to-head redraft. You want week-over-week stability. Stacking gives you high-variance weeks, which sometimes lose you head-to-heads by 40 points. Not what you want.
When you have to reach. Taking the QB's WR3 in round 6 because your QB is Jalen Hurts is trading real value for correlation that might not pay off.
Bye-week overlap. Your stack byes together. If it is your only QB or only decent WR that week, you lose it entirely.
When you already have exposure elsewhere. If Jefferson is on 30 of your 40 best-ball teams, having Justin Jefferson AND Jones stacked with him on 30 teams doubles your positive exposure — but also your negative. Diversify.
Single stack, double stack, game stack
Single stack
QB + one of his skill guys (WR1, WR2, or TE). The baseline. Take when the value lines up.
Double stack
QB + two of his skill guys. Higher ceiling, but you are betting a lot of your team's success on one offense. Use sparingly, and only when you love the offense.
Game stack (aka bring-back)
QB + WR from Team A, plus a WR from Team B (the opponent). Hunts shootouts. If the game goes to 34-31, both offenses feed you and you get spike weeks from all three. My favorite construction for tournament-format best ball.
Common stacking mistakes I see
Stacking QB with the wrong receiver. If the receiver is a possession slot guy with a 4-yard aDOT, the correlation is weak. You want the deep threat and the red-zone target, not the flat-route specialist.
Stacking RBs with QB. RB TDs actively hurt QB passing volume. Negative correlation. Do not do it.
Ignoring negative game scripts. A defensive game where both teams punt on 4th-and-3 five times each is death for your stack. Look at implied totals and pace.
Stacking every QB you draft. Not every offense needs to be stacked. Ineffcient QBs on run-heavy offenses actively hurt when stacked.
My personal rules
Stack in best ball tournaments, sometimes in cash. Rarely in redraft head-to-head.
Only stack QBs I already like. Never chase the stack.
Prefer game stacks for the biggest tournaments. The upside is unmatched.
Do not double-stack unless I love the offense AND the receiver depth.