Gracie is heading along the negative $x$-axis at $.7c$. As she passes George, who is stationary, she punches sharply at him—in the negative $y$-direction—with her fist moving at velocity $(-.7c, -.6c, 0)$, from his perspective. The next day, George is moving along the positive $x$-axis at $.7c$, and Gracie does exactly the same move as the day before.