Rinse the stained area in cold water as soon as possible---do not wait or use hot water, as the stain will set and be more difficult to remove.
Cover the affected area with stain remover or laundry detergent, and let sit for 3 to 5 minutes.
Fold the stained fabric and rub vigorously. Rinse with cold water. Repeat steps 2 and 3 until the stain is gone.
Use bleach on persistent stains. Test a small amount of bleach on an inconspicuous area of the hockey jersey, to make sure color will not be ruined. Add a small amount to the stained area, then rinse and wash as soon as possible.