From Kalbelgarion:

Want to spend the month of March getting hammered? Registration is now open for GrifballHub's Spring 2013 season! Last season we had a record-breaking 2000 players on 400 teams participate in the league. This is your chance to get in on the Grifball action!

Check out this article for more information and to sign up your team. Registration is open until March 15, and games begin the week of March 18. The season will last for five weeks, followed by playoffs.