There is this word that means to force one to stay.
that read backwards, means to force one to leave.
What is that word?
This could be the word:
NAB - which means 'arrest' or 'apprehend'. If a police officer 'nabs' a criminal, they are forced to stay in a prison cell.
Reversed, this is:
BAN - which means 'prohibit' or 'expel'. If a pub landlord (or landlady) 'bans' a person from their establishment, they are forced to leave the premises and not return.
I don't know if this is what you mean but:
TRAP is keeping someone. PART is leaving them.