Dec. 17th update, added a couple of players and a few minor enhancements. If you are still seeing only 2 players in the game, reload the page to get the latest version.
Bookmark this page and come back often, more players and gameplay options will be added.
You player will automagically try to do what's best depending on where the ball is when you click. If you click when the ball is high, but close enough to his head he'll attempt a header.
You can also stop the ball with your chest and let it fall, or you can go for a volley, it's up to you.