Hattrick is an online football game where you trade players and coach your team in competition with hundreds of thousands of opponents playing simultaneously from all over the world.
This is how it works : Hattrick is free of charge. You run your team using your web browser. Matches are played a couple of times a week. You can log on at any time to check the status of your team, issue training orders or game tactics, trade transfer-listed players and more - or just have a chat with the other Hattrick users.
Hattrick is never-ending so when (if) you win your league you qualify for promotion to a higher league the following season (each season lasts for 16 weeks). There are other competitions as well, such as the National Cup, the World Cup (could you become the coach of your national team?), U20 World Cup and Hattrick Masters Cup, just as it comes to national competitions...