Every ex-jock nowadays has dreams of becoming a sports medicine doctor, only seeing patients under 35, hanging out with Kobe Bryant on the weekends, etc. The reality of sports medicine practice in America is a little different.
From what I've seen, very few people are able to get into a practice situation with considerable sports medicine. Most of the Family Medicine/Sports Medicine doctors out there do mostly primary care, with a limited component of actual musculoskeletal medicine. A smaller subset of that is "sports medicine". Anybody who tells you different is lying to you.
One PM&R sports medicine guy who was in a practice with general PM&R docs, and was the official EMG provider for a pro-hockey team said in 5 years he got 1 referral to do an EMG.
This is a best case scenario: I worked in a clinic that was the official provider for 3 of the major league teams in a city. The only one that actually went to the games was the head Orthopedic Surgeon. Rarely, the non-surgeons would provide game coverage. The game coverage component apparently paid quite poorly, isn't worth the advertising benefits, and the surgeons who do it, do so out of personal interest. The teams always prefer the surgeon to the Family Medicine or PM&R doctors. The clinic was run by Family Medicine folks, who did the work up for the surgeons. The surgeons then rounded on the ones who failed surgical management or who had obvious surgical issues. Even in this clinic, maybe 1/3 of the patients were actual "sports medicine" cases. The rest were people with knee arthritis, shoulder impingement, ankle sprain, and back pain. If a pro-athlete came in (which was rare), they were seen by the surgeon alone most of the time.