Preheat the oven to 425 degrees Fahrenheit.
Into a saucepan, squeeze the pulp out of the grapes, saving the skins in a bowl.
Bring the pulp to a boil and simmer for 5 minutes.
Press through a sieve to remove the seeds.
Combine the pulp and reserved skins.
Add the sugar, flour, and lemon juice to the grapes.
Mix until everything is incorporated with a whisk or wooden spoon.
Pour the filling into the pie crust.
Top with the crumb topping.
Bake at 425 degrees Fahrenheit for 10 minutes.
Reduce the temperature to 350 degrees Fahrenheit and continue to bake for 30 minutes.