Yes, I think they need to go the direction of NHL where you are graded on
Position - Being where you're suppose to be, same could be applied to football. Each play you are in the correct position the score goes up, each time you're out of position it goes down.
Team Play - Could go down for things like penalties, missed tackles. Goes up when you simply don't do these things
-There are also in-game goals that the coach gives Ex: We need to force a turnover, or Don't let them score this drive.
Stats - Simply goes up for tackles, ints, fumble recoveries/forced, TDs, etc. Goes down everytime you give up a TD or maybe a big play.
EDIT: It also needs to be weigthed to where a CB gets more XP than a RB in Position and Team Play where as a RB would get more XP for stats.