BACKBREAKER

If you want to do this quickly:
Select the 8 Team League Season Mode
1 minute quarters, 60 second play clock
Difficulty - Easy
You are able to select the teams you want to play against in the league. Go through the teams and select the weakest rated teams to play in the league. Obviously, you want to play with a strong team.
As soon as you get the lead, milk the clock. The computer is really bad on easy. However, if you are losing, just quit to the main menu. Win all nine games (including the Final Bowl - lol) and you will have the achievement!

Update:
If the clock is running and the computer has the ball on offense, you can commit offsides (running into the computer's players before they snap the ball) and the clock will continue to wind down. On the easy difficulty, the computer 99% of the time will decline the penalty. Because the AI refuses the penalty, the clock continues to run without the opposing team moving.

Update # 2:
You accumulate points to spend on free agents to add to your roster after every game. If you use the offsides strategy, listed in the first update above, you will be able to skip spending points on defensive players. I found it to be best to spend points on a good QB, offensive linemen, wide receivers, and a tight end. For me, I did not have any luck running the ball against the computer, so I did not spend any points on a running back.