I think what he is referring to by knuckling a ball is slamming it into a pocket. Personally, I play on diamonds that are new and newish with fresh cloth and cushions. I own a 7' with procut pockets myself. I can tell you first hand if you hit the ball into the pocket without hitting the rails on the way in I have only seen a diamond pocket reject a ball one time in my life. Even that time is suspect as it may have hit the cushion it just happened so fast I could not tell. On the other hand if you hit the rails on the way in tight pockets can be fussy. I have seen a lot of tables that would allow you to hold two balls together and slide them right into a pocket. I can tell you that with procut pockets you will not be able to do that. I believe the shelf depth also will contribute to balls getting caught up as you say. The deeper the shelf depth the tougher the pocket according to what I have read. In reality, I tend to try to only hit the object balls hard enough to pocket them yet not hard enough to be able to get my cue ball to another pocket unless absolutely necessary. Then again I am still working on my pattern play.