Squat, and twist left to hold the dumbbell on the outside of your left leg.
Lift the weight diagonally across your body, ending twisted to the right with the dumbbell above your head. Pivot on your left foot as needed. Return to the start position for one rep.
Focus on rotating from your torso, keeping your abs stabilized throughout the movement.
You can also do this move with a medicine ball, at a cable station, or with a kettlebell.