Learn to move through difficult emotions during your sport by practicing moving through them in your yoga practice. If you have trouble meditating because you "cannot sit still," do it anyway-do it past your comfort zone and then you will be able to push past your comfort zone off the mat too. Set a timer and sit or lie down for that amount of time, even if its just 3 minutes--it will help you! Or if during your asana (posture) practice, you zone out and don't pay attention to what you are doing, not only will you eventually injure yourself, but you are not benefiting from your mind training that an asana practice provides. During your physical practice, when the mind wanders, bring it back to what you are doing. Then you will notice as you are about to run that rapid or push up that hill, when your mind wanders and then you get scared and feel like giving up, you can bring your mind back to what you are doing. In the moment, there is no fear.
Here are a couple more great articles from my favorite Yoga Journal writer, Sally Kempton:
What Are You Resisting?