There is a tendency for members of the gallery to offer advice during the game, comments such as "Great drop shot, more of those", "Well played, more like that ",
"Keep them in the corners" etc.
If I am marking, I tell the culprits that any advice can only be given between games, and not within earshot of the opponent. Occasionally, I have said if gallery coaching persists, the culprit would have to leave the gallery.
Gallery spectators generally look at me in disbelief !
Please clarify what can be said from the gallery in between points in a game.