This can only be done with a fumble recovery or interception, and you need a clear path to the endzone. While running it back aim for one of the front corners and make it so your guy hits the red pylon. Then it should say that you've returned an interception for a Touchdown, but then you'll be lined up 1st and goal and then you have to get it in the endzone to score your second TD. It takes accuracy but usually adds 13 points.