A default occurs when a defendant fails to show up to court. This can happen even when a defendant is late to court. You most certainly can be arrested if you are in default.
Typically, after a default is entered, the judge will issue a "warrant" against a defendant. That warrant allows any police department to arrest the defendant and bring him/her back to court.
All warrants are logged into a database called the Warrant Management System (WMS). The WMS is accessible to all courts and police. Police officers routinely arrest people for outstanding warrants. For example, if you are in default from a court but are stopped in your car for speeding, there is a good chance that the police officer will arrest you and bring you to court - not for the speeding infraction, but because of the warrant.