Although this is not a traditional yoga pose, I have found it to be particularly helpful in many flows that I have both practiced and taught. Given its spin on the traditional Virbadrasana I it more opens up the inner thighs and helps to stabilize the pelvis more in preparation for other poses further in the flow. This summer I have specifically enjoyed working with it in a flow that involves coming into Virbadrasana II and exhaling to Ardha Chandrasana then inhaling into Crescent Warrior, then repeating to Ardha Chandrasana. I like this flow for many reasons; two of the main ones are 1. it helps to gently stretch the breath, and 2. it involves my favorite leap of faith.
How to Practice
Crescent Warrior is very easy to work with. Starting from Virabhadrasana II with the right hand extended, exhale the left forearm to cross your lower back. Then inhale the right arm up the kiss the ear. This should give you some sensation along the side body of the right side.
Working from flow above. Once in Virabhadrasana II, exhale leaping off the back foot and coming to Ardha Chandrasana. Inhale set the back foot back down, while bring the left forearm along the lower back and bringing the right arm up to kiss the right ear.
Feel grounded in the back edge of the back foot, and energetically ground in the front edge of the back foot. Keep the knee in line with the ankle, and pushing towards the pinky toe. For the most part the feet and legs should have the same stance as Virabhadrasana II.
Which ever way that you enter into this pose, remember to mirror that on the left side.
If you can not reach the fore arm along the lower back, just use the hand. Gently let the arm progress along the lower back over time, and do not strain to get it there right away. Also you can bring the back hand down along the back leg for a deeper stretch in the side body, however having it along the lower back helps to open up the shoulders and chest for arm balances.
Just as with any standing poses it is always recommended to have at least one seated pose to go along with it. Crescent Warrior more prepares you for more poses that require the pelvis to be steady, the inner thighs warmed, and, depending on the movement of the arms, for arm balances further in the flow. Following Crescent Warrior it is recommended to do one set of Surya Namaskar, at some point soon after.