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SSCAIT 2016 round of 8 - first half

The SCCAIT round of 8 was played last week as 4 best-of-3 matches. The loser of each match is out and the winner moves on. Today I’ll go over the first 2 matches of the 4, from the first video.

LetaBot vs WuliBot

This match was easy to call and I don’t have much to say about it. The forecast: LetaBot will wall in and zealot-heavy Wuli will be unable to cope.

As it turned out the first game was even less interesting—Wuli froze up and died with one pylon to its name. The second game went to script. Wuli’s zealot rush is strong but risks being hard countered, and that’s what happened.

ZZZKBot vs Iron

ZZZKBot’s 4 pool also risks a hard counter. And Iron knows a counter, but it is not as hard as it could be. When Iron sees the danger it stops any tech beyond barracks (often canceling gas) and pulls SCVs to block its entrance. As soon it can it builds a bunker behind the SCVs, and if it succeeds in getting marines in, it is usually safe.

As always, Iron knows some excellent micro tricks. When it has enough SCVs blocking, it will sometimes mineral walk damaged front SCVs back through its own blockade to the mineral line. That means that the SCV right-clicks minerals so that it passes through any intervening units, allowing Iron to rescue damaged units in front without opening its blockade.

Game 1 was on the level-ground 2-player map Heartbreak Ridge, ideal for the 4 pool. Iron saw it coming in time, got the bunker up, and got a marine into it, pulling nearly all SCVs to block. It was close, but Iron held and had more income. When it was safe, Iron switched back into its usual aggressive strategy and won easily.

Game 2 was on Icarus, a 4-player map with ramps which is not as good for the 4 pool. But the bases turned out to be close together, which is favorable for the rush. Both bots scouted each other in time. This time ZZZKBot broke the ramp and won—Iron got a bunker up but could not get a marine into it. ZZZKBot showed impressively smart targeting with its lings, switching smoothly between hitting the empty bunker and chasing away any terran units that came close. At one point zerg split its lings into 2 groups, one to chase the last marine and one to disrupt mining.

The deciding game 3 was on Empire of the Sun, a 4-player map but without ramps and with a wider entrance to defend than Heartbreak Ridge. ZZZKBot sent its overlord scout the right direction and did not need to make an extra drone to scout, which strengthens the rush slightly because 2 more zerglings fit under the supply limit. 3 drones mining are enough to keep up constant zergling production; more drones produce extra resources that are only useful if the rush fails, when the rusher is generally lost anyway.

But in any case, this time Iron narrowly held and won. Apparently the result depends more on random factors than on favorable or unfavorable conditions!

With good worker micro, it is more efficient to hold the rush in the mineral line, rather than at the entrance. Tscmoo knows how to do it. In pro games, attacking zerglings have to be cautious around workers and only pick off stragglers, because the workers fight so effectively.

Tomorrow: The second half of the round of 8. Maybe I’ll catch up with real time by the time the finals broadcast on Saturday!


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LetaBot on :

Usually you defend a 4 pool with a bunker close to your command center and mineral line (usually between you CC and refinery).

The danger of putting a bunker far away from this is a zergling runby.

The other disadvantage is that your barracks is usually far away from your bunker. By the looks of it, this is why Iron bot won game 1 and 3, but lost 2.

Igor Dimitrijevic on :

The reason why Iron builds a bunker at the choke point is to avoid then one hundred things that may happen if you let early Zerglings come in in numbers by your Command Center.
As I see it, top 4-pool ZZZKBot uses quite a small number of tactics when it gets its Zerglings at destination. This does not mean it has to, nor it always will. BTW, some clever Terran bots exploit the fact that ZZZKBot's Zerglings are often obsessed with Marines, accepting any amount of damage from the defending SCVs while they try to reach the Marines. Obviously, they don't have to. I once saw a TvZ game between two famous pro-gamers. The Terran player sim-citied its bunker and barracks to fend off a 4-pool rush. I don't remember who won, but what I do remember is that Zerg's threats were everywhere, everytime, and of every kind. As a programmer, I can easily think of ways to implements many of these threats, if I were to make a 4-pool bot. But I can't imagine a way to counter all of them, especially if I don't know them in advance. Too many sub-games, each requiring domain specific expertise. Another point: while this game was very close, I have the feeling the balance is not the same when it comes to bots: while both move at quite the same speed, Zerglings are much easier to control than SCVs, they are smaller, and they have a higher rate of fire. This makes Zerglings much stronger than SCVs when heavy micro is involved and possible. Bots can easily micro units by units, frames by frames, which pro-gamers can't. This makes me believe the bunker at the choke point may be a safer option for a Terran bot, if possible. Obviously the intent is not to allow any run by. Hence the blocking SCVs. Even when the bunker is completed, some SCVs keep blocking the entrance. A lot of these SCVs will die or be damaged, I'm ok with that. Even if some Zerglings manage to run by the bunker, sniping Marines can go out and chase them quite safely. Unfortunatly, last version of Iron has some issues with Marines's behaviour I didn't notice. It should otherwise win 9/10 games against 4 pools. Building the Barracks a few frames sooner should help getting a bunker in time. But Jay is right about the random factors: Iron's blocking SCVs do fight quite a strange way sometimes. This is due to Starcraft's internal collision issues, plus SCV's move latency. Some things hard to deal with...

krasi0 on :

Great analysis and very informative, Igor! Thanks!

Jay Scott on :

I think it’s a good point that what pros do is not necessarily best for bots, even as an end goal. Their abilities are too different. That said, I also think that defending a 4 pool far from the mineral line is a hard sell. Anyway, may the best plan win out!

Igor Dimitrijevic on :

Well, I consider it a hard sell too ;)
Especially when I consider the implementation which is not trivial at all. There are many aspects, each of them causing a defeat if not handled well enough. But they are not that many and I know them all. I just can't say the same with the bunker at home variant. So to sum up, Iron's strategy to fend off early Zergling rushes is hard to implement, I warn. And it involves very close games and might even be a loosing strategy in the end. But the idea here is to cut the tree of possible executions, and thus, in the end, the developement time in this sub game.

Jay Scott on :

I like that way of framing it.

krasi0 on :

Yaaay! Finally the (first part of the) Ro8 analysis! The wait was worth it. I love your joking comments :)

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