Final answer:
The most effective method of immobilizing a shoulder injury as described is using a Sling and swath. It supports the arm and restricts movement to aid in pain reduction and immobilization.
Step-by-step explanation:
The most effective method of immobilizing a shoulder injury with a noticeable anterior bulge, like the one described where a 20-year-old man has collided shoulder-to-shoulder during a soccer game, is A) Sling and swath. This method supports the arm, restricts movement and helps to reduce pain and swelling by immobilizing the joint. Spine board immobilization, traction splint, and air splint are not typically used for shoulder injuries. It's important to note that shoulder injuries can be complex and the method of immobilization should be followed up with medical assessment and appropriate treatment.