The best way I have found to do this is to set offsides to 0 then use your SS to line up directly behind the QB. When he snaps the ball you will sack him. I was averaging about 20 sacks a game. This also counts for tackles so you can get your 140 tackles this way as well. If you use your hitstick you may get less sacks but do cause more fumbles which can get you the forced fumble achievement.