My crust cracked! Any idea why?

The cracks can mean your pie pastry was too dry, or at least the spot where it cracked was dry. If pastry dries out on the surface before baking, moisture produced inside the rest of the dough can't escape as easily. It has to "force" the issue, and that leaves you cracks. If you happen to have any of the crust dough leftover, you can thin that a bit to fill in your crack, and give it a few minutes in the oven to set. You can also mix up a paste of flour, half that flour amount in soft butter and a pinch of sugar, and use that to fill your crack. Then again, bake until it sets. It won't look like the original crust, but fortunately the filling should cover the mishap and nobody will know but you.