Well the answer to that is easy. They want inconsistant racks of 9 ball so it's a bit harder to run consecutive racks. I applaud it because i like to see safety battles and skill. If you can run like 6 or 7 racks in those circumstances it's much more fun to watch because they will have to shoot...
I just saw Filler pot a ball (not alongside the rail) which hit the first diamond...it still went in. He and de commentators were very surprised it went in.
Alex got a warning or something for not hitting the break the right way. Can't find the specific rules on it. 2 balls past the head string...