Can they do this?

[CO ump]

Originally Posted by GarthB

1. Let's say a pitching change is being made. Coach then tosses ball to F3 who throws "grounders" to F4, F5, and F6 who throw the ball back to F3.

Is this okay in your games?

This happens often. Yes

Originally Posted by GarthB

2. Pitching change is not being made, just a conference. Again, coach then tosses ball to F3 who throws "grounders" to F4, F5, and F6 who throw the ball back to F3.

Is this okay?

Don't remember it ever happening, but Yes


Back to OP this is totally a judgement call.
Let's say F6 had been shaken up in previous half inning, got on field late and didn't have chance to test the arm. Coach sees him working the shoulder and comes out for def. conference with ball and tosses to F6. At this point I know this is not a ruse to warm up the next pitcher, no problem.
If F1 is struggling, no one is warming up in bull pen, Coach comes out for conference with ball in hand and tosses to F6, I may be inclined to judge that F6 is warming up, not allowed.
If you don't allow it and your judgement is wrong there is no real harm done.
If you do allow it and indeed F6 is warming up and 2 batters later F6 enters as pitcher then a disservice has been done to offensive team.