Why does my standing leg hurt when I'm doing the warrior 3 yoga pose?

You should never feel pain when performing any exercise. If you continue to feel pain, you should discontinue or modify that exercise, and seek the guidance of a medical professional. Movements that are performed incorrectly or in excess can cause inflammation. Reconsider the form that you are using when performing this yoga pose. Make sure that your hips are level and that you are not locking or hyperextending the knee of the standing leg. Try modifying the pose by extending your back leg and both of your arms at a diagonal. Keep a slight bend at the knee. In this pose, you should only be slightly hinging at the hip of the standing leg. Draw-in the belly button toward the spine and focus on consciously contracting the butt and abdomen. You can also try using a chair for support and to take some of the weight off of the standing leg. If modifying this pose does not alleviate symptoms, then discontinue this pose.