Take a look at this submission from Peter.   A great example of a [tag]throwing[/tag] [tag]drill[/tag] for [tag]how to play baseball[/tag] that can work with all age groups.How to Play Baseball

Teaching Freshman players proper throwing:

I have done this (trick) Drill with our freshman [tag]baseball[/tag] players at the beginning of each season. It has really improved their throwing.
Have them partner up in twos or groups of fours. Put down their gloves and baseballs. Hand out a football to each group and have them throw it to each other.(give them a quick demo on how to hold and throw the football)I will do this for 10 min. 2 or 3 times in the first week of practice. (it will improve there arm motion, follow thru and accuracy)

Back-up/grounder drill:

I use this drill/game towards the end of a practice. works on reacting to & fielding grounders, and backing up plays.     Have 2 lines facing each other(distance apart depends on level of players,   space available, indoors or out).

X X X     B       P …………..P         B       X X X

X players in line
B back up player   (fields a missed ball)
P player (fields grounder and throws one back)

“P” starts drill by throwing grounder to other team.
1 point is given to throwing team every time a ball gets by player.
Another point is given if the ball gets by the back-up player.

Set boundaries to the right and left (out of bounds) I use the basketball court(paint and free throw line as the box for fielder and back-up player.

Rotate people through “P” fields throw, returns throw and goes to end of line. Back-up player moves up to “P” position, X player moves up to back-up position.

This drill starts out slow and intensity increases as teams try to get the grounder by the opposing player. It also speeds up for the same reason.

Excellent drill for working on fielding, reacting to ball, moving right/left, fielding and popping up quick ready to throw and being there to back up a play. Plus it’s good competitive fun(loosing squad picks up equipment at the end of practice)