Zerg: Stopping a 4-gate. 

A conventional 4-gate will complete at 6:15 if executed properly.  In the lower leagues or in the hands of a less experienced player, the 4-gate may finish a little later. 

A conventional and properly executed 4-gate will hit your base anywhere between 6:30-7:00. 

Spine crawlers take 50 seconds to finish building.  If you build these, you must start before the 5:25 mark to be safe. 

Roaches take 27 seconds to spawn.  Zerglings take 23 seconds to spawn. 

This means that Roaches (The Power Unit) takes nearly the same time as the Zergling (The Panic Unit). 

And some fluff. 

The 4-gate consists of 3 different unit compositions. 

The All-Stalker approach.  Mass speedlings are the counter here.  Make minimal roaches. 

The All-Zealot approach.  Roaches are the counter here.  Do not make speedlings. 

The Stalker-Zealot mix.  Speedling and Roach mix is needed.  Pure roach or pure speedling will not work here.  If he has a lot of zealots, make more roaches.  More stalkers, and you need more zerglings. 

There are several things indicative of a 4-gate push.  Here they are. 

The cybernetics core will finish at roughly 3:35. 

This means that Protoss must have enough for 4 chronoboosts.  at the 3:35 mark.  If you scout around this time frame and he has max, or close to maximum energy on his Nexus, he is saving up for warptech. 

At around 3:38, protoss should have a stalker.  You will want to scout a little earlier to see what he is doing. 

At around 4:30, or when his warpgate tech is half finished, Protoss will plant down his 3 additional gateways.  You must send an overlord to his base to scout the timing of those warpgates.  If at around 4:30 you see 4 gateways, you must start to prepare.  You have a little less than 2 minutes to prepare. 

Preparation. 

Start scouting for his proxy pylon.  You should have already gotten the speedling upgrades and perhaps 2-4 zerglings at the start of the game.  Scout with them. 

Do not stop scouting.  Take the xel'naga towers. 

Split your zerglings up and have them scout the areas near your base.  Finding the proxy is crucial.  Do not forget that protoss may plant a proxy in a hidden corner within your own base. 

Plant one or two spines.  Or maybe 3.  You must start before the 5:25 mark to be safe.  Make a second queen. 

A roach warren takes 55 seconds to complete.  If you scouted properly, your roach warren should go down in preparation for a 4-gate at around 4:30.  This means it'll finish at 5:25.  This gives you 45 seconds to build units. 

Build roaches first.  Power units are important.  And then some lings.  From there, build whatever you can. 

Engage around your spine crawlers.  Only engage out of range of your spines if you are confident that your current army composition is enough to push his 4-gate back. 

If you previously scouted his proxy pylon and destroyed it, keep pushing.  Protoss will be forced to retreat and he will no longer be able to keep attacking due to economical constraints.  Take your second, and defend.  Remember to scout for any second pylon that the protoss may have planted. 

If you were unable to scout his first pylon, be prepared for continued harassment.  plant another spine or two, make more roaches or lings (depending on his composition).  Use your second queen for spreading creep.  Push your spines closer and closer to the edge of your base and prepare to break his harassment. 

here's a question for you aehu, i'm finding most platinum players will not blindly 4 gate (with the rare exception) and instead will have a standard build they use untill they scout the zerg going 14-15 hatch.  with that in mind what is the best counter to a 4 gate with the economic advantage provided by the extra base.  but a smaller army

Edit: I say platinum because 3/4 of the players i've been facing are platinum but i find the same can be said for gold league as well. 

Most Protoss build orders revolve around this to some degree.  This takes around 2:44 to complete. 

In a properly timed 14 pool 15 hatch build order, the hatchery should go down at around 2:38.  In a properly timed 15 hatch fast expand, the hatchery should go down at around 2:10.  For a 15 hatch FE, I plant my spawning pool at 15 supply.  This brings me to 2:41. 

The key here is to keep in mind that the earliest 4-gate aggression in a standard build order is at the 6:30-7:00 mark.  The timing is somewhat similar for a 3-gate aggression, so for the purposes of this write-up, I will focus on a 4-gate. 

Plant my gas and roach warren at the same time, around 4:40.  Get overlords and plant spines (5:15 timing).  At your natural, use your first 25 energy to spread creep. 

Starting at the outermost edge of my ramp, build spines next to one another going across your natural. 

By 6:20, you should be able to complete 5 spine crawlers, 3 roaches and 6 zerglings, if not more.  This is more than enough to ward off any 4-gate aggression.  Plant more spines as needed. Remember that since roaches take less time to spawn than spines take to complete, plant your spines first. 

At this point, two things can happen:1] Protoss camps outside your base and refuses to let you leave. Don't be overly worried about being locked in two bases.  Get your lair tech, and get mutas.  Protoss has no counter against mass mutas, and on two bases, this is a distinct possibility.  Continue to mutalisks and take a third expansion, while denying and harrassing Protoss with your mutalisks. The only tech that I can think of that Protoss will/can go to stop this type of aggression is zealot/archon.  Blink stalkers do not counter mass mutas.  Keep up with your upgrades. In this video, Destiny goes mass mutas and wards off a 6-gate in a similar manner to what I am talking about.  6-gate is aggressive and although the scenario is different in this game, the strategy that Destiny uses applies to a 4-gate contain. In the event that Protoss goes zealot/archon, maintain your mutalisk count and continue to harrass.  Start getting roach upgrades and continue to make roaches.  Plant an infestation pit.  Infestors take 50 seconds to complete.  Pathogen Glands take 80 seconds.  Start Pathogen glands, wait 31 seconds and start getting infestors. 

2] Protoss continues to push. Be aggressive with your spine crawlers.  Unlike other static defense, spine crawlers can move.  Continue to spread creep and keep pushing out with roaches and spines.  Solidify (for lack of a better word) your defense, and continue to macro up.  Protoss should be behind in terms of units lost.  Use this to your advantage.  Follow up using scenario 1. 

Keep in mind that using a mutalisk-centric play will force the Protoss player to gas dump on archons and templars.  The Protoss player will be forced to mineral dump on chargelots.  Use fungal growth in conjuction with superior roach and mutalisk numbers.  Win. If you have the economy for it, mass broodlords are an acceptable counter to the archon/chargelot unit composition. 

If Protoss elects to continue with deathball, reference the video linked in scenario 1.  Here is the video again.  Go either mass mutas, or hydra/roach/corrupter mix.  A-move to victory.