For dynamic stretching of your hips area, I strongly recommend completing the following stretches, (15-20 repetitions for each leg/hip), warming up before pitching in a game or a bullpen session. You will increase your leg and hip flexibility during your pitching motion, reducing the risk of injuries.
Swing your leg in a side way fashion in front of the other leg (abduction to adduction). Then move your leg in a swinging-kicking motion, (knee extension to hip extension). Lastly lift your knee to above your waist in a sideway or adduction movement.
Alternating these dynamic stretches with both legs will fire up and strengthen your hip muscle complex, while activating the synovial fluid, lubricating the hip joint.
Be sure to maintain a good posture.