3TS is a set of new organizational, where and how-to-play, field rules:
Most standard softball/baseball rules of play apply (hitting, fielding, pitching, etc.), only the rules of organization change to accommodate 3 teams at a time instead of 2 (see below and other pages). Plus seasonal scoring is added.
A full game has 3 teams of 5 players each (thus only 15 people are needed to play, not 18 or 20, and teams need only gather 5 players each (this is a big deal in small towns, intramural sports, adult and work leagues, etc. - often it isn't easy to get 9 or 10 players together on time, for every game. Organizing and getting only 5 people to show up each time is much easier), As such:
There are always 10 players on the field, plus 5 batters (no substitutes except for injury).
Infield 5 = 4 infielders + catcher. Outfield 5 = 4 outfielders + pitcher (the pitcher is considered an outfielder). And there are 5 batters.
During play, the batting order only applies to those not on base! If a batter is on base, his/her turn at bat is skipped and not made up. The next batter is up instead.
To promote development of players as batters, no extras or substitutes are permitted in the batting order: not playing = not batting (it promotes development as a batter, for those who get on base more don't bat as much as those who don't).
For convenience and to introduce the ideas of field positions at the start and during each inning of the game (while retaining some traditional reference), teams can be referred to each game as Home, Visitor, and Away.