Recently I had a game where I went for a risky Hatch-First build. Except before the hatch was close to being completed, the Protoss walled off my main's base with pylons exactly like the picture below.
Then he continued to create photon cannons behind this wall. How do I combat this? I tried getting roaches up and moving spine crawlers up, however my spine crawlers miserably failed as he broke through one of the pylons and moved them to the spaces not covered by my creep in my main. How do I prevent this? How can I stop this after it has begun? Killing the probe I am sure would be the priority. This, however, can be a difficult deal when he protects the probe by the cannons behind it.
As a side note, I understand that many tournament maps have a neutral supply depot to prevent just this. Here is the link to the article.
Best Answer
There's a very popular way to break out of this wall in called the drone drill.
Essentially you will be puling most/all of your drones and making them all focus a single pylon. It's very micro intensive, but you can break out of it very quickly.
Psystarcraft has a tutorial on how to do this here:
Edit: As tenfour noted, this does not work on all maps. Psy also notes it near the end of the video where he mentions that you need to use the right mineral patches, the wrong ones will not allow you to pull this method off.