My Own Fly Ball
Here's one you can incorporate right into your daily throwing warm-up. After the players are warm, have one line back-up so everyone is throwing farther than the base path (*note: adjust the distance for younger age groups). Start all the balls with the players lined-up on the foul line.
Have one player call out a "Ready, Go!" or some other indicator to start.
Once the players call, the entire line throws their ball up in the air over their own head to simulate a fly ball. In other words, they are throwing a pop up to themselves.
When the ball comes down, the catch it and fire it over to their partner.
Things to look for...
Proper catching technique: Don't allow players to basket catch the ball or catch it down by their stomach. Everyone should be catching the ball up above them and out in front. Encourage the use of two hands on the catch.
Proper Positioning: Players should throw the ball up high enough to allow themselves time to get into proper position for the catch. If they need to move back or forward, make sure they are moving their feet and not just staying planted and reaching for the ball behind them or out to the side.
All players should be stepping to the ball with their glove foot on the catch. They should not catch the ball with their feet next to each other or with their throwing foot forward. Catching the ball with feet side by side or the wrong foot forward will result in a slower, weaker transition into the throw. The step with the glove foot should land just before the catch is made. Just as a player should step to the ball on a regular catch (throw being made to them), they should step to the ball on a fly ball or pop-up catch as well especially if they have a throw to make immediately following the catch.
Proper Throwing Technique: You may also looking for proper throwing technique after the catch, but this drills is primarily to give the players reps catching fly balls/pop ups with correct positioning, footwork, and catching technique. Encourage players to keep the ball down on their throw, not throw it way up in the sky as younger players may tend to do. Again, depending on skill level, you may want to focus on one aspect at a time and not bombard your players with feedback on EVERYTHING at once.