I sent in a support ticket on this once. Here was my question and their answer:
QUESTION: Quick question for my own clarification:
If I am running a zone defense and choose to double team an opposing player, my understanding is that my defense becomes a box-and-1, where 1 player is assigned to follow the opposing player all over the court.
When I do this, (1) does the defensive player in the matchup correspond with the offensive player's position (i.e. def SG always shadows off SG) and (2) how does the defensive player's ATH/SPD/DEF individual ratings factor into the success of the double team (is his defensive prowess still the product of the averages of his teammates or is it based solely on his individual ratings).
ANSWER: Grimace,
When playing a zone, you can think of double-teams as more like "key on this player". So a doubled player would often draw multiple defenders from the zone. It's not exactly like a box-and-1, which is a combo man/zone defense.
When playing a zone, any defensive factors are essentially averages of the 5 guys on defense, regardless of double-teams.