When on defense go to 3-4 and select "Base". When on the field, select your outside linebacker and move him close to the line without crossing the line of scrimmage. Once the QB snaps the ball, use speed burst to run around and sack him. This will work almost every time unless there is a TE were your LB is located.
When on defense, press Start to pause game play. Go to the options screen, choose "Penalties" and set everything to "0" except for fair catch interference. Resume the game and go directly in front of the quarterback. When he snaps the ball press Down + Tackle to sack him 99.9% of the time, unless he runs out of the pocket.
When on defense, press Start to pause game play. Go to the options screen, choose "Penalties" and turn off offsides and encroachment. Select anyone and go across the line next to the QB. When he snaps the ball, run up to him and tackle him.