Preheat oven to 350 degrees F (175 degrees C).
Smash berries. Stir in sugar and ¼ cup flour. Pour filling into pie crust.
Smash walnuts into small pieces. Stir in brown sugar, ¼ cup flour, and shortening with a pastry blender. The mixture should be crumbly. Sprinkle streusel over pie.
Place pie on a baking sheet and bake in preheated oven until crust is golden and filling is bubbly, about 45 minutes.