No manual blitzing with linebackers or defensive backs. Now, you can call on anyone to blitz from any position on your defense, it's just it can't be YOU controlling him. The reason is that the blocking AI can never pick up a human opponent properly. This is cheap as well, don't do it. There will be no compromising on my part with this rule.
The one exception is that if you are playing linebacker/CB, and you are covering the field and the QB BREAKS THE POCKET, you can go after him. As soon as you see the QB scrambling to the right or left, you can go after him. If you have a CPU controlled player CLOSE to the QB or already past the offensive line and you want to take control of him, feel free to do so! Load up on that hit stick!