@ Red Devils 21 - this question has been asked of admin before and they have so far been unwilling to answer.
Based on my observations, I
think determination works something like this:
For ATTACK: a defensive player (D and DM) will be more likely to become involved in attacking play if he has a high determination score (than one with a low score). This is less important for midfielders, even less important for attacking midfielders, and not important for forwards.
For DEFENSE: the opposite is true. Attacking players (AM and F) are less likely to track back and become involved defensively with a low determination score. This is less important for midfielders, even less important for defensive midfielders, and not important for defenders.
However, after a player has been on the pitch for 60 minutes, stamina becomes just as important as determination; even a highly determined player will need the stamina to perform these "secondary" roles.
NOTE: This is just my deduction based on observations of many matches. I could be completely wrong, but I would bet there is at least some truth to these conclusions.