Sports agency revolves around three key aspects - sales, relationships and contracts. As a result it is, at least in part, well suited to lawyers. Traditionally many sports agents were former lawyers, although in more recent times the emphasis has shifted from athletes wanting a safe pair of hands, to requiring someone who can bring them lots of deals. Showing them the money isn't just in the films. The importance of being able to negotiate the best contract is still vital, but in a difficult market the real challenge is to secure the contract in the first place. The most successful agents are those that can sell the athlete and win the deals.
Once the sponsor or commercial opportunity has been won, then the value of being a lawyer really kicks in. Most agents aren't lucky enough to have a Beckham or a Woods and many deals are for sensible money. The agent is then loathe to spend much of his/her commission, usually 20-25%, on outside legal fees.
Football agency is strictly regulated these days with agents only entitled to represent footballers if they have passed an exam and licensed with the FA. Lawyers are an exception to the rule and are automatically entitled to carry on agency activity.
Sports agency is an exciting and glamorous world to be in. You are able to mix business with pleasure. However it is not necessarily all as glamorous as people perceive it to be. There is a lot of running about after your clients, you are literally on call 24/7 and there is no such things as a weekend or holiday. Many clients do not think twice about calling their agent in London from their hotel room in the US at 3am to ask where their taxi is, and the novelty of mixing with famous people soon wears off. There is an enormous amount of travelling and other agents are permanently trying to pinch your clients. It is a fun job, but be lucid to the reality of the downsides from the outset.
You are really going to have to have experience in contract law, and even then a contract lawyer with relevant sports experience will be at an obvious advantage - the sports world generally thinks that lawyers are too conservative anyway, and so an agency or management company will be looking for someone who understands the nature of the industry.