Can they do this?

[umpire99]

I was calling a FED game last night where the coach of the defensive team requested time out and came to the mound to talk to his infielders. As he approached the mound, he threw a ball to his F5 who played catch with F6 as the coach talked with the pitcher on the mound. I told him he could not do that. He stopped without questioning me, but after the game, I decided to look this up to be sure. I cannot find anything anywhere that does not allow this. Any help?