You can't intentionally drop an infield fly in some umpire's interpretation. It is an unfair advantage to the offensive team. It falls under making a mockery of the game. But I still recommend trying it when you can because you never know how they will interpret it. You have to sell it for it to be legal with most crews. Umpires do not have to vocally call it but they should raise their hand. Even if not called it is still in place.