He can move to any country that doesn't have debt collection agreement with US (assuming he's from US). Like Philippines or New Zealand. Or just make himself judgement-proof. Convert his savings to Bitcoin, quit his job and work cash jobs. Court cannot force him to earn less.
Unpaid child support will result in an arrest warrant in many states. The debt itself may be civil, but it's a crime to avoid the court mandated payments.
My father in law was in a coma for a while and the child support payments stopped and he went broke from the lack of job and medical bills. They arrested him multiple times after that because he wasn't paying. Of course that gave him a criminal record and made it much harder to get a job.
