What roster do you use? I use Bedwards roster and have good numbers as regards PiP and final scores, both me and my opponents rarely reach 100 points, most of the time we finish around 85/95, last game against Dallas they scored only 29 points in the first half, i was Denver!
At the beginning I also had trouble defending, try not to stay glued to your opponent, leave a little space so that you can both contest the shot and cut the drive, depends on whether you're defending a good shooter or not, and remember, your goal is to ALWAYS stay between the ball and the basket and ALWAYS contest the shot with LT or RS