You can join a team when the team captain has invited you to the team. The team Captain needs to invite players to the team on a tournament-by-tournament basis so the invitation must be accepted at the beginning of each league season/tournament.
If the invitation is from a team you are familiar with, you can press ACCEPT. You cannot leave a team whose request you have accepted (except by asking the captain to remove you - depending on tournament rules in question), so it is important that you only accept a pre-arranged invitation.
From the image below you can see what the team invitation looks like on the SportsGamer front page.
If you're looking to get in contact with teams looking for players, we suggest you to post yourself as a free agent in the assigned forum thread here (EU PlayStation), here (NA Xbox) or here (NA PlayStation).
