You defend this build by doing what Light said. You float your natural into your main. You pull a bunch of scvs to deal with the initial attack because you won't have enough bio yet and then you hold on for as long as you can until he's defeated. There's no obvious timing for when this is, but trust your 1.5 base Terran to outproduce a 1 base Protoss eventually. After he has expended himself it's a casual walk across the map to go end his shitty stalker army with your medivac + bio. Some Protoss might try to just expand instantly and pretend to be going full all in so keep tabs on just how many units he does have, try to build a sense for it.
Smaller tricks include:
1) when you scout 2 gas and a few stalkers early, strongly suspect this opening. Keeping scouts near the cliff can be one way to confirm it. Most protoss will only build stalkers early if they are doing this build as sentries cost precious gas and zealots do nothing.
2) scan and pick off observers whenever you can. Every observer you snag kills 1.5 stalkers that he wants to make instead and buys you more time.
3) Prioritise building marauders. Stim marauders rip stalkers up, and concussive shell is very useful when chasing the speedy bastards
4) keep your buildings away from cliffs. Your tech lab for stim must be in a safe place deep in your main and close enough to pull scvs for quick repair. If he snipes your stim research then you're going to have an extremely hard time beating his attack.
5) bunkers don't do anything. Salvage them/don't bother.
6) this is a big one so it gets put in all caps and bold FOR THE LOVE OF GOD BE CAREFUL WITH HOW YOU STIM AND DO NOT PURSUE!. So many times a terran will be in a great spot vs this and he fucks it up by killing 20% of his army with stim and chasing a protoss who just "LoL Blinku!" and loses nothing. Stim is great for punishing shitty blinks but it's never something you just throw out. Also, chasing blink stalkers before you have an overwhelming amount of units is fatal. He just blinks away, warps in another round of stalkers and then jumps on you once stim wears off. Stim again? Great! That's 40% of your army you just killed before a stalker fired a single shot. Cool.
If you're playing a 1/1/1 style and your opponent opens these then you have to decide whether you want to all in and risk getting backstabbed and playing that horrible game or trying to expand and try to avoid losing anything to random blink pokes. I dunno it's fairly miserable.
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