During the England Vs Australia rugby union international on 18th November 2017 at Twickenham, Michael Hooper scored a try for Australia that was disallowed due to him being offside. According to the BBC's Guide to the offside law...
A player is offside if he is in front of a team-mate who last played the ball AND they actively try to play the ball
When Tevita Kuridrani kicked the ball forward ("played the ball") then Hooper was clearly offside as he was ahead of the kicker, however, he did not play this ball! When Marika Koroibete did play the ball, Hooper was behind him and hence in an onside position.
So, was Hooper offside? A video of the try can be found here