A-Rod played defense according to his stats.

As long as a player had at least 1 assist at a position, the game does not penalize him for the amount of innings played - it uses his stats, just as it did for A-Rod.

I had the same results with Troy Glaus at SS a few years earlier. A-Rod wasn't a fluke, he was an example of how the game uses defensive stats.

There probably are some "cut-off" numbers the game won't allow a player to get beyond - that seems to be the case; but within pretty wide limits I "think" the game tries to simulate the actual player stats as it did for A-Rod.