My name is XXXXX XXXXX I'd be happy to answer your questions today. I'm sorry to hear about your situation.
If you signed a piece of paper agreeing to pay for damages in exchange for him agreeing not to press charges against your son, that unfortunately is enforceable. The exception is if you can prove that he threatened you or your son in order to make you sign it - in that case, it was signed under duress, and you can argue that you did not voluntarily make the agreement. Keep in mind that he can still seek a judgment against your son for causing the damage, if he can prove it, whether you had signed that paper or not.
If he does sue for damages, you can countersue for assault for the abuse, which is an intentional tort
. You'd be able to claim medical bills, pain and suffering, and punitive damages
. You can also file criminal charges - domestic violence
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