I honestly believe Fields will be fine. There's something about newly signed free agents when they come to Toronto after inking a big deal (I'm talking 5 million per year on average and greater),they always seem to get off onto slow starts.
This happened with Turkoglu most recently when it took him until mid January in the infamous(post game interview with Jack) game vs the Knicks. Fields role is smaller so I'd expect him to pick it up alot sooner,but this just 4 games for a player who's new to the team and system.
Also people are forgetting he's has just 2 years of experience under his belt and encountering his third different coach and system within that same time span. He's still developing as a pro basketball player. At his best he was so good that the Knicks refused to part with him in the blockbuster trade with the Nuggets for Carmelo Anthony. Have a little patience,Casey and co. will find away for Fields to become more productive