The Softball Relay Throwing drill is a good drill to practice not only throwing but also to practice the transition to throwing. The reception and transition to throwing should be on the glove side. Have the players practice that without the ball before beginning the drill.
Softball Relay Throwing Drill
Have the players line up in a line stretching to the outfield. Have the first player throw the ball to the glove side of the second player in the line. The player receiving the ball should be set up with their glove in ready position slightly on the throwing side. This will give the thrower a good target. Do the same for the rest of the players. This solidifies the proper location for the relay throw and also teaches quick turn and release of the throw.
You can vary the distance of the players and you can also use ground balls. For example, have the first player throw a ground ball to the second player who fields it, turns to their glove side and throws it to the third player who turns to their glove side and throws it to the fourth player who turns to her glove side and throws it to the fifth player who receives it. She then throws a ground ball back to the fourth player who fields it and goes back the other way the same as the first time.
When it gets back to the first player, she runs to the other end of the line and becomes the 5th player after she flips the ball to the second player moving toward her who becomes the first player. You can make this a relay where the winning team is the one who gets the first player back to where she was at the beginning of the drill. Make this softball throwing relay drill fun and make it competitive which will be closer to a game like situation.