5. A, B, C, and D each hold a soccer ball and simultaneously pass the ball once, with each person able to pass the ball to any of the other three. The probability that each person still has one ball after one pass is $\qquad$
5. $\frac{1}{9}$.
$$
P=\frac{3 \times 3}{3^{4}}=\frac{1}{9} \text {. }
$$