Preheat oven to 350 degrees. Grease an 8-by-8-inch glass baking dish.
In a large bowl, toss apples, blackberries, sugar, and 2 tablespoons of flour. Scrape filling into baking dish.
In a small bowl, toss oats with remaining ½ cup of flour, nuts, brown sugar, and cinnamon. Add butter and cut into flour mixture.
Sprinkle topping over filling and bake for 35 minutes, until the filling is bubbling and the topping is browned. Let the crisp cool for 10 minutes before serving.