If a citizen marries and applies for a green card for the spouse and the spouse comes to US and is abusive how can the citizen send this person back?

Contact the INS. They would be able to help you.

The person cannot just be "sent back" simply because the US citizen has changed his or her mind about the marriage. If the person has the conditional green card, the US citizen can refuse to file the joint petition to remove the conditions, but that does not guarantee that the person will not be able to obtain the permanant greencard. Once a person has legally immigrated to the US, it takes a lot for him or her to be deported. Any US citizen can bring a person to the US, but he/she cannot have the person deported for personal reasons. Marriages fail every day. Whether the ex is allowed to stay in the United States or not is not the concern of the American spouse, but of the INS officer who gets assigned to the case.