Tie, clip, or outline at least one target (you can do two or more if your backstop is big enough) to your backstop at approximately receiving height for your age group. Have your players line up in one or two lines an appropriate distance from the target. Hit or roll grounders to your players and have them make full arm throws at the target(s). This drill stresses correct fielding and throwing techniques. You can make the drill fun by keeping track of how many times players hit the targets (with correct fielding and throwing techniques employed).