Mark Twain, one of the funniest English authors, says in his Adventures of Tom Sawyer, "Work consists of whatever a body is obliged to do...Play consists of whatever a body is not obliged to do". That is, work is what we must do. Play is what we must not do.
Physics has a different definition of what Work is. Using this definition, you can convince your parents and teachers that you are working, when you are playing sports. Let's quickly find out what the definition is!