I had this last week. I was trail (3-man) and I blew my whistle just after ball was at free-thrower's disposal, I then stepped in and brought situation to lead's attention, and he called for the ball back. We had players switch places and resumed administration of free throw(s). No one had a problem with it. If questioned, I would have said I noticed it before ball was at free-thrower's disposal but I was slow in blowing my whistle.
