I can agreed with cat Harrison on the rating based on player interacts with the ball. just yesterday, my opponent's goalkeeper saved 6 attempts, and he got rating 9. few days age, i won 4-0, my opponents used 3N-4-3 and all his DC got rating 8. - hahahahah

Usually, i make sub based on level of tiredness of players or when i change the formation. sometimes, when whoever miss the chances, i take them out.