Has an AFL game ever ended 31-18?
Yes. AFL has seen a final score of 31-18 2 times. It first happened on June 21, 1902, when Carlton beat Sydney, and most recently on June 27, 1908, when Sydney beat Fitzroy.
That makes 31-18 the 2421st most common final score out of 6,607 that have ever occurred in AFL. One point away, 32-18 has happened never and 31-19 has happened never.