Everybody on the team needs to be a good thrower. Some young players have no trouble zinging a ball right to where they want it to go. But others need careful step by step instruction.
Note to Coaches: The steps here are broken down in Tai Chi style - the end of each step is a check-and-correct position. However, that is a teaching method only. You do not wants stops or pauses or hitches in the actual throw. The most obvious correction to look for is in shoulder angle - they should be in line with each other and the target, not equidistant.
Get your feet under you - very important after fielding the ball.
Line yourself up. Two invisible ropes - from back foot through front foot and from back shoulder to front shoulder - go straight to target.
Plug into the ground, on the inside balls of your feet, shoulder width apart. (From outfield, do a crowhop - back foot crosses front, then front foot forward - before plugging in.)
Find the target early - with both eyes.
Check and correct.
Take ball from glove with ball resting on palm of throwing hand. (We used to teach "palms away / thumbs down, not any more.)
Bring both arms up - elbows to shoulder height.
The throwing arm will swing out and up easily, allowing the fingers to get on top of the ball.
Throwing arm never bends in more than right angle (90) - wider is better (120).
Glove arm up and opposite the throwing arm - with either glove to target or elbow to target.
Front leg comes up. Check and correct.
Back foot rolls in and up to toes, back knee tucks forward.
This opens hips, to let torso come around, which brings throwing arm forward.
Front leg will move forward for balance, keep it pointed slightly to the throwing arm side, knee relaxed.
Plant the front foot out front but don't worry too much about stride length. (Fielders might stride half their body length, pitchers 3/4 of body length or a bit more.)
Throwing elbow should still be shoulder high, angle between arm and body between 90 and 110. (Arm too high causes shoulder impingement.) Check and correct.
Keep the glove in front of the chest. Glove turns over - flip and pinch - and elbows come in as the throwing arm comes forward. (We don't teach glove tuck any more because it pulls the body open too soon, but we don't want a lazy glove arm either.)
Weight shifts forward over bent landing knee. (Not a deep bend, just relaxed enough so the hips are free to let the upper body rotate through.)
Arm comes forward, elbow extends, wrist delivers back spin.
Throwing arm sweeps across body to opposite hip, using contact with the body to stop safely.
Glove side still up out of the way - throwing arms goes under. Check and correct.
Get this fielder throwing right well before trying to pitch.
More advance instruction by Richard Todd and other instructors is available at WebBall.com.