First and the foremost, obtain a law degree. In most cases, a law degree would be enough to support you with your cause. Without a law degree, there is no way you can dream of becoming a sports lawyer.
Specialise in spots law. Not many universities offer sports law as a specialisation subject. If you university does, make sure you go for it. In case it does not, you can opt for courses that somehow relate to sports law.
Be a media man. Indeed, becoming a sports lawyer has a lot to do with being a person who can speak in front of the camera. You will often see sports lawyer in interviews and press conferences, defending their clients and the like. You need to have such capabilities in order to become one.
Gain experience as a sports lawyer by joining a sports law firm or working with a sports lawyer. Again, you might not find a lot of specialised sports law firms. Your best bet would be to work with firms that mostly take up cases of sportsmen.
Make sure you keep progressing as a sports lawyer. Keep opting for certifications in the field to gain an edge over others. Since the field is relatively young, there would be many competitors in your way. You have to make sure you stand out of the crowd.
Remember, sports lawyer is different from a sports agent. While sports agent do take care of cases related to sportsmen but are mainly there for promotion, sports lawyers are just specific to their duties.
You need to be an entertainer to become a sports lawyer. If you are a person who does not like being involved in media stories then probably sports law is not for you.