Go back and forth, in a way

Once upon a time, there was a mischievous dog named Rufus who loved to play catch with his owner, Billy. Rufus was always excited when Billy would throw the ball, but sometimes he would get so excited that instead of bringing the ball back to Billy, he would run away with it!

Billy would have to call Rufus back and forth, trying to get him to drop the ball so they could keep playing. One day, Billy’s dad watched them play and said, “It’s like Rufus is wagging back and forth, deciding whether to bring the ball back to you or keep it for himself.”

From that day on, whenever Rufus would hesitate with the ball, Billy would call out, “Come on Rufus, don’t be a WAG!” And that’s how the term “WAG” came to mean going back and forth in a playful and indecisive way. Eventually, it made its way into crossword puzzles as a popular clue and answer combo.