Time, dedication, and a bit of money. Regardless of the sport, it seems that the training and leagues that are available for those working towards a college scholarship (evolving into a professional career) are not very cheap. whether it is equipment, training facilities, travel leagues or gym memberships, the costs add up. Furthermore, a lot of time a effort needs to be put forth. You must desire to be a professional athlete entirely, and focus all available time towards that. a good coaching network of strength, agility, speed and conditioning is a plus. Along with a good soccer coach and work ethic. I am sure a bit of luck has to come into play as well.