From Onset Developer Wiki
Called when a (local) player presses the key to go in or out of the aim state. You can return false in this event to prevent the player from aiming.
You can use CancelAimImmediately to stop the player from aiming if he is in aim state already.
true if the player wants to aim, false otherwise.
AddEvent("OnPlayerToggleAim", function(toggle) if toggle == true then return false -- do not allow the player to aim end end)