Think of it as real football. you can't always get sacks in a game. Although a majority times a team will have at least 1 sack. But it takes patience. Try using blitz packages. Use a player blitzing, move him up just a little bit, then after the snap, let cpu control it for a second, then what I do is I use sprint and strafe joystick (usually right or left depending on where I think is the best route to the qb). Usually what happens is the pocket collapses and it results in a sack, int, incompletion. But change it up every so often. If the starter is injured and they put a scrub qb in, blitz often using this method. Just be patient.