Start up a quick play game on Rookie difficulty. Choose a team with a strong/fast running back such as the San Francisco 49ers or the Philadelphia Eagles. Both of those teams have a solid offensive line as well, and that makes running the ball even better.
Just keep calling running plays while on offense. If your starting running back is fatigued, he will go to the sideline. Keep note that if you hand off to a back-up, those yards will not cumulate to the total of your starter.
This trophy should pop at the end of the game. (To be honest, I can't remember if it pops right when you hit 200, but I'm 95% sure it pops at the end)