Leaving Early - how is it handled?

[Justme]

I need guidance (ASA rules) - You see a base runner leave early.

Is this an automatic out or an appeal?

If it's an automatic out how do you handle it?

Would you call them out following the completion of the play or as soon as you see them leave early?

What if they would have made it to the next base as a result of the play anyway?

Thanks