Starcraft AI blog

“Cheese” is a put-down, and the proper definition of “cheese” has a flavor of “stupid trick that you shouldn’t have beaten me with.” But who cares? I can pretend to be objective, and define a cheese strategy as: A surprise strategy which is all-in and fails if the opponent scouts or expects it. If the opponent pays a cost to stay safe against cheese, then game theory says that you may want to take the risk to cheese a certain percentage of the time to force your opponent to pay. The cost can be the need to stick to rush-safe strategies, or only the cost of scouting for proxies. It depends on your risk of losing with risky cheese versus the opponent’s cost to stay safe, of course.

Another definition of “cheese” is: An all-in opening that sacrifices economy to an extreme degree. It doesn’t say how extreme, but it’s closer to how people use the word in practice.

Against a human you can’t play cheese often, because it fails if expected. By definition! But bots are not good at expecting things. Most bots are vulnerable to cheesy openings and only a few have strategy learning that may be able to learn to defend, so—why don’t other bots cheese more?

I’ll talk not only about cheese by my definition, but also other risks or tricks that seem cheeselike. I was only pretending to be objective.

cheese that current bots try

• 4-pool, 5-pool, 6-pool
• cannon rush, cannon contain
• dark templar rush (not cheesy, but risky if it’s very fast)
• hard zealot rush (not cheesy, but all-in when protoss commits to it)
• SCV rush (in some LetaBot versions, and formerly by Stone)
• BBS (two barracks before depot, played by Tyr)
• marine rush (10 barracks into infinite marines, UAlbertaBot)

other cheese

• offensive sunken in ZvZ (ASPbot did this in 2011)
• proxy hatchery
• proxy 5 rax (LetaBot used to do this with bunkers; variations are possible)
• proxy factory (make super-early vultures to kill workers)
• barracks float, factory float (into the enemy base)
• proxy gateways (which can mix with cannons)

The offensive sunken in ZvZ can work when combined with another attack. By itself it just fails if the opponent reacts. The natural other attack is, of course, a 4 pool or 5 pool after you scouted with a drone.

You can make anything at a proxy hatchery. In the early game you make zerglings or sunkens. If you get burrow, a drone may be able to hide in the enemy base for a long time before proxying. If you somehow remain unscouted in the middle game, you might build lurkers. In the late game, drop a drone in for creep to support a nydus. All these are risky cheese plays; if scouted, they lose resources for nothing.

I think it’s strange that we see zergling rushes and marine rushes with BBS, but no zealot rushes with early forward gateways. On a 2-player map, building gates near the enemy base at 5 and 6 supply kills most bots effortlessly. Many other forward and center gate variations are possible, at least up to 9-9 center gates.

In another point, if you’re making an all-in rush, there’s no disadvantage to bringing some workers along for the fight, no matter your race. Terran of course can make bunkers. Protoss can make a proxy shield battery (typically in the enemy natural) to support the rush—the pylon is “free” since you need it anyway.

It’s also strange that we see no in-base proxies other than cannon rushes. Many bots will pop like a balloon when you hide a gateway or two in their base. Against a terran bot that doesn’t scout its base, you can hide a probe and make a late in-base proxy gate for dark templar. Or try this BBS variation as terran: Scout early, and build your first barracks in a distant part of the enemy base, near a cliff. Build the second barracks beneath the cliff and float it up beside the first.

Some slower tech rushes are so risky that you could call them cheese. 1-base lurker is one example. AIUR’s fast 4-zealot drop is another.

cheeselike tactics

You can block stuff with a worker/pylon/etc. It’s not cheese, but it’s tricky and cheeselike.

• gas steal
• mineral steal
• manner pylon
• pylon block of terran add-on (especially the first machine shop)
• block natural hatchery/nexus (common against 12-hatch)
• block opponent from walling
• block opponent’s exit (on maps with a small exit like Heartbreak Ridge)
• pylon prison, a crazy blocking trick

Bots still know how to steal gas, but I think they've given up on doing it because they stopped seeing advantage. I think that once bots can read and react to the opponent's strategy well enough, they should go back to stealing gas, but only at times when it will channel the opponent's strategy in a direction that the bot can exploit. Opponent modeling helps. If you know that your opponent’s tech causes you trouble, then steal gas to delay their tech.

You can order your scouting worker to mine an enemy mineral patch, and then the enemy can't mine it at the same time. You can steal 8 minerals or stop mining early and start again. It's mild harassment that slows down enemy mining slightly. If you also steal gas, you can steal 8 minerals, steal 8 gas, steal 8 minerals... which is not useful but is funny.

Manner pylon is advantageous if done at the right time and place. It can cause the opponent to lose more minerals in mining time than the pylon cost. The reason we only occasionally see manner pylons in pro games is that pros prevent it when they care, briefly idling a worker to stop it if necessary. Manner pylon can be worth it in the early game, and it can be worth it later in the game at expansions. I think it's safe to guess that very few bots will react correctly to manner pylon; they will not know how to prevent it, and they will lose more mining time than necessary when it happens. Bots with fixed build orders will mess up their timings. It can be a little tricky to pull off a manner pylon, though, because you can only build it when the spot is free of enemy workers. Good players can predict when the spot will be free and slide through the mineral line with the right timing to build the pylon in passing.

Cheese is healthy for bots because opponent bots need specific knowledge to respond well, and there are many kinds of cheese so much knowledge is needed. But cheese can also be difficult to play well. Current bot cheese is plain cheddar next to pro artisanal cheese. Tomorrow: Cannon like Nal_rA.