Which of the following rules applies to base runners in NCAA softball?

The rule that applies to base runners in NCAA softball stipulates that runners cannot run into a fielder who has the ball. This rule is in place to ensure player safety and to promote fair play on the field. When a defensive player is attempting to make a play on a batted ball or receiving a throw, other players must avoid unnecessary collisions. This rule helps protect players from injury during what can be a very physical game.

While other options touch on important regulations within the game, they regard different aspects of gameplay. For instance, some scenarios in NCAA softball do allow for sliding, while there are specific rules about when a runner can leave a base. The rule about wearing helmets applies universally to players when they are actively engaged in game play, but it is not specific to base running alone. Hence, the emphasis on avoiding contact with a fielder in possession of the ball stands out as a critical rule regarding base runners.