Use the Gatorade Sports Performance: Football Training Camp-Recovery. You will need to get the first challenge to be at 8/9. to do this keep playing until you score a point. Then you can quit. This will count as 1 of the 9. Once at 8/9 you will want to quit as soon as the game allows which is at 33 seconds. You will hit start then quit. You will receive 4 stamps for every time you do this. just reload the training and repeat quitting out at 33 seconds.
Estimated time is 3 hrs to get from 50 to 100.