Tim Duncan isn't the best free throw shooter. I just watched his form on one, and his right foot pinches in. As a result, the ball bounced of the left side of the rim. Straight line to the goal, and the shot falls. It's that easy. I know this because I had the same problem about a month ago. After serious thinking, I fixed it in my head, and then translated it to the basketball court. The first night I tried the new form, I think I hit 16 of 20 free throws. What coach wouldn't be happy with that?