Win a game without being scored against in Easy mode.
The most important thing to remember for this, is that the clock runs until you select a play. So, march down the field to get the lead, and let the little play-clock timer almost run out before choosing your play every time. Once you score, hold them on Defense and the clock will run while you pick Defensive plays as well, so drain it again as much as possible. After you hold them once and get the ball back, repeat the same slow play calling until you get down by their endzone but do NOT score. You already have the lead and are going for the shut out, so more points do not really matter. Keep the ball close to the endzone, but don't score and when the ball becomes "Critical", throw it away or get tackled and they will get the ball back right there and have to go the length of the field to score on you. (It does not matter in easy mode if you lose a player from a critical ball explosion; they will be replaced on the next play.)