BUG - Yorick wall block me outside

you need skill to do that

So here is what happened, when the ring comes up while you are stepping in the area you either get pushed in or out depending on where the center of your model is, now in your situation you were more outside so it pushed you out, the thing is his ring was right next to the terrain so you got pushed in that area. What happened is you were pushed into enough of an area that the points directly in front and behind you were too small for your hitbox to move to so you just couldn't move, this also happens with any other terrain creation skill like Pillar of Ice, Crystalize, Weaver's Wall, Emperor's Divide, or Cataclysm. This is literally a perfect storm of events that happens once every billion games and you just happened to get screwed by it.