Substitution rules in Softball allow starters to re-enter the game (unlike baseball). For example, say my first baseman is a vacuum cleaner with her glove, but slow as molasses as a base runner. When she gets on base, I can substitute one of my bench players as a pinch runner and then re-enter my first basemen afterwards. Game starters can re-enter the game one time in the same place in the batting order in which they started the game. If they are substituted for a second time, then they are ineligible for the rest of the game. A bench player that enters the game as a substitution is ineligible once she leaves the game (she cannot re-enter like a starter can). In our first baseman example, the pinch runner is out of the game for good when the first baseman re-enters the game.
The situation where players in the field switch positions with other players in the field, otherwise known as a defensive swap, is not considered a substitution as no new player enters the game. Players can swap positions inning to inning, even pitch to pitch, with no penalty. Note, though, that a pitcher returning to pitch within the same inning is not allowed any warm-up pitches.
An exception to Softball substitution rule is the Courtesy Runner. A team can use a Courtesy Runner to pinch run for a pitcher or catcher any time they reach base. Use of a Courtesy Runner does not count as a substitution, so when the pitcher or catcher assumes their position after the end of the half inning, their appearance does not count as a re-entry, and the player used as a Courtesy Runner is still available for use as a substitute later in the game. The Courtesy Runner used for the pitcher has to be a different player than that for the catcher, and must be a player eligible to be used as a substitute. If a player being used as a Courtesy Runner becomes a substitute, then another eligible bench player can become a Courtesy Runner.
I like Softball substitution and Courtesy Runner rules a lot. Because starters can re-enter the game, I am much more likely to substitute when I have a big lead – if our opponent manages to scrape back into the game, I can re-enter my starters and (hopefully) regain control. This allows for more sportsmanship between teams as I can tell when my opponent “calls off the dogs” and they can tell when I do the same.
Courtesy Runners can be “equalizers” for a team from a small town (like mine is) with perhaps not as much depth at catcher or pitcher as other teams. I can rest my pitcher and catcher when they get on base. In tournaments on hot summer days where we play three or four games in a day, resting my best pitcher and catcher with Courtesy Runners can mean the difference between a deep run in the tournament and an early exit. Plus, using Courtesy Runners gives players who may not otherwise get into the game a chance to play, all without burning a substitution or a starter re-entry. Getting as many girls in a game as possible while still winning is the best of all possible scenarios, in my book.