This is one of those great [tag]baseball drills[/tag] that works on a couple of things at the same time.   As a [tag]baseball coach[/tag]–we all like those!!   I use this mostly for when I need my players to coach first base. I coach alone so of course I am on third!!     Rotate the players through coaching and base running.

Set up:
Players lined up at the plate as the batter(just take off running)
One player acts as base coach.
1st baseman playing his position.
Coach is at the mound or somewhere in the close infield to make the throw to 1st.
1st baseman makes the play as usual while the base coach is telling the player to stay or go.
Coach can make the throw as easy or difficult as desired to challenge the first baseman. Base coach is telling the runner to go on an overthrown ball.

You can also add scenarios such as a bobbled [tag]baseball[/tag] in the outfield, or errors at other bases.   This is good [tag]baseball drill[/tag] to start with and it teaches your players to be vocal while they are coaching 1st and is great work for the first baseman.