A: I was surprised to hear that your school’s football team lost the game yesterday.

B: Indeed. Usually a key player on the field, our star running back seemed to be mailing it in yesterday afternoon.

Note: This idiom literally means “to send something somewhere or to someone by mail.” It also means “to perform a given task, duty, or activity with little or no attention, effort, or interest.” A similar term is “to phone it in.” Perhaps the usage comes from the practice of sending your teacher or employer a mail or giving them a phone call to ask for a day off. When an actor, singer or an athlete is just going through the steps to get on and get off, it is not very pleasant to watch and the audience can tell that they are mailing it in.