For a new grading system, can you somehow adjust to take note of the player's role? For instance, in a blitz situation, the DB is probably not going to play a ton of trail without lots of help. If it's a zero blitz, they are going to play off. If the blitz doesn't get home, the QB may complete a pass. Sometimes the DB is coached to play in such a way to allow a pass but limit yardage with a good tackle. That, to me, is an important thing to note. You may give up a 10 yard play, but it was by design that you were taking the risk.