Unethical practice: casting director books multiple actors for same small role, pays only the one confirmed onset. Rest wait unpaid — cheap casting at talent's expense.
On set, it works like this: The Casting Director calls three, four, sometimes five actors, books them all for the same small role — a waitress, a police officer, whoever — and tells none of them that others are also being considered for the same part. They are all supposed to show up at the shooting location. Whoever actually stands in front of the camera gets paid. The others watch, wait all day, and go home unpaid. This is bit-legging, and it only works because newcomers and actors in smaller roles often don't know how to defend themselves.
The logic behind it is cynically economic: Why worry about the right casting when you can simply haul everyone in for selection? The director reserves the right to decide at the last moment. Some justify it with "flexibility," others with "we want to see all options." In reality, money is saved on casting, and the risk is shifted onto the shoulders of the performers. You'd prefer not to participate — but when you're young, hungry for credits, and the job pays nothing, you turn a blind eye and hope to be one of the chosen few.
Professional Production Guidelines — such as the codes of actors' unions — have long forbidden this. Union productions have clear rules: booking is booking, regardless of whether the role is cast differently. For indie crews and low-budget productions, bit-legging remains widespread because checks are rare and actors are often too afraid to complain. Your reputation for being difficult to work with is worse than losing a day for free.
On set itself, you see the drama: The waiting actors sit in the corner, trying to appear relaxed while the chosen actor is being costumed. Sometimes the reserves are called in for small tasks — an ad-lib in the background, an extra role — as minor compensation. But money? Travel expenses? In most cases, zero. The ethical line is clear here: Booking means commitment. Anything else is exploitation with a scientific name. Those who work professionally book one person per role — or transparently clarify that it is an open on-site casting.