Penalty rates are based on NFL stats. Defensive backs aren't offside very often, but it happens.

We will never have ratings for players for a couple of reasons. 1) A player's performance is represented by complex formulas with many parameters. For example, for running backs there are like 20 parameters that define their performance. There isn't an easy way to boil it down to a single rating. 2) Player selection is mostly done before the NFL season finishes. I don't calculate the performance parameters until after the season in over. 3) The game is intended to test your actual ability to build an NFL team based on your knowledge of players and ability to predict how a player will perform into the future, similar to how an NFL GM would have to project these things.

The valid point is that for some positions, it is really hard to know how your players are contributing to success or failure. As mentioned we want to provide more of that information on the next re-write of the simulator, to be completed at a time to be determined.