Generally speaking, the upright meaning of the Fool is that of birth, new beginnings, fresh starts, journeys and exploration. It can also mean not looking where you're going, being naive or foolish, or a potential disaster if you don't stop staring at the stars and take a good look at what's directly ahead of you.
1) Opposites: If we were to go for a simple, opposite meaning, the card might mean an ending and/or wisdom.
2) Blocked: More apt is the blocked interpretation. If the energy of the Fool is all about starting something new, going somewhere new, then blocking that energy means that the querent is having difficulty starting anew, moving, seeing the world with fresh eyes.
There is also an implication of being stuck, uninspired. The Fool, if you will, is sitting at the side of the road with blisters on his feet and rocks in his shoes, unable to go on his way.
3) Upside-down: What if we turn the image upside-down? I'll use classic Rider-Waite here--but in reversing the image, interpretation, of course, will depend on the deck.
The cliff edge is hanging over the Fool and his feet have no real purchase. We might say that he's falling, dropping off from under the rock to free fall through the yellow sky. Everything, the sack, the dog, tumbles with him.
We might well interpret this as the Fool (in Rider represented by Air), getting completely lost in his head, in hopes and imagination, in talk of what he's going to do, completely surrendering to the sky, with no way to actually walk toward anything, even disaster. This, we might say, is the Fool doomed to Foolishness that makes sense only to him. He is not in the real world and whatever he proposes cannot be made real.
Curious about this card when upright? Go to our Tarot Card Meanings.