The XML Soccer PHP Library by Volodymyr Chukh is a PHP Client Library for the XML Soccer API. The XML Soccer API is a web service that collects soccer data and makes the information available in XML to subscribers of the service.
Here is an interview with Scott Gimpel Founder and CEO of FantasyData.com. The site used to be known as NFLdata.com and provides NFL statistics. The site claims to have almost 25 million API calls /month during football season with over 300 developers working with it's API.