A Goblin riding on the back of a Warthog will attack you, as other Goblins on foot flood the area as well. And that something greater quickly shows up on-scene thereafter. You need something greater to break through. There's a huge sealed door at the northern end of the courtyard, and when you approach it, the game will tell you that not even Goblin grenades will do the trick here. Run forward as you begin this stage, and you'll drop down into a little courtyard.
