TvZ Hatch Block

      -Rally the 10th SCV to your opponent's natural. To be clear, that's the one that brings your supply to 10 when you start building it. The 9th SCV is the one you rally to build your first depot.

      -Build your first barracks on 12 supply, like a normal opening. On ladder, I'd consider a low-ground wall-off, for reasons to be discussed later.

      -You're going to need another SCV on the map to help bunker rush your opponent's third. Rally either your 12th or 13th SCV to your opponent's third. Ideally, take a roundabout route so your opponent won't see this SCV coming.

      -You have enough money for the engineering bay at 13 food, but that will delay your 14th SCV. Wait until 14 food to build it. If a drone comes down to the natural to try to kill your SCV before it gets the block, dance around in the area where the hatch gets built until you have money to build it.

      -When the barracks finishes, get an OC and rally your first marine across the map to your opponent's third. If there's an overlord along the way, don't stop to kill it.

      -There really shouldn't be much trouble getting the bunker down. Bring one more SCV across the map around the same time as your marine finishes, to increase repair rate and as a backup if drones manage to kill one of the ones you have down at the bottom.

      -Zerg hides a drone by the natural well before he can afford the hatchery. He then waits for my SCV to check up in the main since I haven't seen a drone come down to build a hatchery, and then he builds it while my SCV is on the ramp.

      -Zerg brings 2 or more drones to try to kill my SCV before it can plant an engineering bay. In a similar vein, I plant the engineering bay and he brings 3 to 4 drones to kill it as quickly as possible.

      -Zerg has a drone follow the SCV that built the engineering bay across the map so it can't build a bunker, then expands to his third. The hope here is that I didn't bring another SCV so I can't threaten his third.

      -Zerg expands to his third, and tries to kill the bunkers threatening it before they can finish off the hatch with drones, lings, and maybe queens. This might be the best response I've seen, but it is generally very map-dependent.

      -Zerg expands to his third, cancels when he sees the bunkers, then builds lings to kill the engineering bay and takes his natural. This puts him at least mildly behind, since he loses money on the hatch cancel, and all that money was tied up in a hatch that never finished.

      -Zerg expands to a hidden location. Here he is hoping that I'll assume he decided to one-base all in.

      -Zerg one-base all ins. This is pretty self-explanatory.

      -Always build the engineering bay. Don't run up into the main to see what he's building. The engineering bay is built at 2:15; there's nothing interesting going on in his main at 2:15, and if there is, you'll know because he didn't expand. And even if he doesn't send a drone to take the expansion, build the engineering bay anyway. It'll help you spot any 1-base aggression coming, and it'll help prevent him from taking that base if his third base attempt fails and he tries to take his natural.

      -Don't fight the drone that comes down to take the hatchery. An SCV always beats a drone in a one on one fight, but he has lots of reinforcement drones nearby to help with the fight. Just dodge around in the area where the hatch is built until you have the money for the engineering bay.

      -Keep the hatch-blocking SCV alive if possible. If he only sent one drone to stop the engi bay block, this should be easy. When he's attacking your SCV as it builds, stop it from building when it has 10 HP left and right click the minerals in your own natural. If he sent multiple drones from his main to stop the engineering bay, you may have more trouble keeping this SCV alive. If it dies, send one more SCV from your main in addition to that one at 12 or 13 supply.

      -Rally your first marine directly to your opponent's third. When he's defending with drones he'll try to stop the marine from making it into the bunker. This can make your push fall completely flat. If you can get the marine in without being stopped, do it. Bringing your 2 or 3 SCVs to defend the marine on its path can help a great deal. If you don't think it will make it through, let it wait a little further back until you have another marine or two to drill through with.

      -If he doesn't try to take an expansion, send everything home and take a safe bunker position on your natural. By "safe bunker position," I mean the bunker positions Terrans learned to use when 2-base all-ins became the Zerg standard to punish 3 CC builds. Also send one of your forward SCVs to scout for hidden expansions.

Notes: The aggressive bunkers in the mineral line are excellent for defending, but it is relatively easy for zerg to block marines from ever reaching the bunkers.

The hidden bunker at the top left is not well-protected, but it is less likely to be spotted, so you could, for instance, distract a drone with a fake bunker that is cancelled below while building this bunker above unseen.

The bunkers at the bottom right are walled against the edge, so zerg has to run around the other side of the hatchery to get to anything behind them (obviously a useful situation). They are, however, relatively exposed.

The other possible third:

This hidden position at the top left is fairly secure because of its low surface area, and its relatively easy to get marines to it. The adjacent aggressive bunker further restricts zergling and drone access to this hidden bunker.

The lower pair of bunkers are less restrictive in surface area, and less accessible to marines. They do, however, have a longer run-around distance for drones and lings, and they have more interesting places to put repairing SCVs. Personally I prefer the higher orientation.

Note that this base does not have a lot of places to hide repairing SCVs, and there are no special formations with which the SCV can be entirely protected. On the other hand, this base is easier to bunker rush than the alternative third because the marines can more easily reach the bunker without being blocked.

Notes: The hidden bunkers at top are more restricted in terms of surface area. The aggressive bunkers at bottom have more surface area, but also create more enclosed areas for SCVs and are more accessible to a marine coming up from the ramp at the bottom left.

With the large number of spaces to keep SCVs, this is an excellent base to bunker rush. You might consider bringing more SCVs than you would otherwise tend to when bunker rushing this base. The biggest obstacle is getting the marine to the bunker safely.

Notes: The bunker with the isolated SCV placement is the obvious one. This, however, is not especially easy to reach with a marine.

The hidden bunkers at the top left are relatively easy to reach with a marine; the bunker at the bottom right is the easiest to hide from a drone. Note that the bunkers at top left form a wall between the geyser and the top edge, so attacking lings must run all the way around the geyser. This means you can place repairing SCVs in the crevasse behind.

In general this is not a very easy third to bunker rush. It is relatively accessible to the zerg, and relatively inaccessible to marines.

3rd by watchtower: + Show Spoiler +
3rd in opposite main's natural: + Show Spoiler +

-Send the SCV at 10 like normal, and rally it to the natural of the main in the opposite corner. That is, if you spawned left bottom, rally it to right top.

-When your SCV is about halfway across the map, send one of your SCVs to the edge of your main closest to the middle. You're checking for an overlord sent across by the Zerg player.

-If you see an overlord, divert your course to the close -by-air main's natural. Otherwise continue running to the other main. You should have time to run up his ramp and check for creep just to be sure he spawned there.

This way as long as he sends the first overlord directly to the close-by-air main (and he will 99% of the time), you can find him every time. If he doesn't send the first overlord across for some bizarre reason, your chances are still 50%.