Pull a switch is a term used to describe the act of exchanging one thing for another. It is often used in the context of trading goods or services, but can also be used to refer to the act of changing something from one state to another. For example, pulling a switch on a light switch would cause the light to turn on or off. In the context of a crossword puzzle, the term SWAP (4 letters) could be used to describe the act of exchanging one letter for another in order to complete the puzzle.