Big Waaagh is an army that relies on building stacks of Waaagh Points, which slowly applies stacking buffs until every unit in your army becomes Big Green Murder Machines. There are many ways to generate Waaagh Points, from landing charges to heroic actions, and especially by having units stuck in at the end of combat.
That last method is what has created the technique known as Waaagh Stacks.
A Waaagh Stack is when several units (typically a screen and several heroes) are tightly confined near each other so that when you engage with one, you engage with them all. In most situations, this would do more harm than good—a single unit tying up multiple units (restricting their movement)—so what’s the benefit in doing this?
The answer lies in Waaagh points and how critical they are to your army! For each of those units stuck at the end of the combat, you get an additional WP. Even if they can’t do damage (shamans, wurrgogs, etc.), they’re still stacking buffs for the rest of your army. The difference of 2-3 WP early game is huge, often reaching your powerful buffs a whole turn earlier, allowing you to take control of the game much sooner than your opponent might have expected.
Even outside of the early game, an early WAAAGH can be detrimental to your opponent. This technique has allowed me to hit full stacks, twice, in multiple combat-heavy games. Getting +1 to charge, cast, and hit at the top of round 2 instead of round 3 has cascading results as your army chops your opponent down instead of dawdling and trying to accumulate resources.
Many of the risks from the Waaagh Stack technique are mitigated by natural functions of the army. For example, Orruk characters tend to be pretty tough and fighty, so a few stray hits reaching over your screen are very unlikely to actually kill your units.
Additionally, mechanics like the Wurrgog stare and teleports from the Big Green Hand of Mork can get you unstuck and ready to fight on your own terms. This prevents your opponent from gaining a strategic advantage off of their plays while you reap the rewards.
Every small edge matters in a game of Age of Sigmar, so remember, Stay Stacked or Get Clapped.