When it comes to bodyweight abs exercises, crunches aren't always the way to go. In fact, research has shown the classic crunch isn't even that effective since it doesn't activate all of your core muscles.
High-Plank Bird Dog Start in a high plank position. Brace core and raise right hand and left foot off ground, like a traditional bird dog. Return to starting position and repeat on the other side. Do 10 reps on each side.