Great post by Jude. Here's another angle on things.
Possibly during the first 6 balls you are thinking of ,posistion, making the balls and not thinking about winning.Your possibly not even thinking stroke or mechanics as everything is just flowing by feel and quite naturally. On the last three balls you (could be?) start thinking about winning, or perhaps maybe even the fear of losing.When fear enters the equation, the back arm tightens and fear even effects your eye sight.
I suspect it's a mostly a mental dilemna as I know the symptoms and suffer from them as well.Craving so much for the admiration and respect of my peers brings on unwanted pressure.I'm just dieng to be able to shoot like I can in practice.
I've started to read some books on the mental game and claiming the last three balls as a fault of yours only goes to further the subconscious to repeat the failure again and again.Never ever talk about your failures with the last three balls again...EVER!!!
Tell yourself (with affirmations) that you are the best last 3 ball shooter in the pool hall.Write it down on cards even if you have to. Say it over and over and see if things change.Fake it till you make it.When you do successfully run out the last three say to yourself "This is me!"When you fail to do so, say to yourself, "I'll do better next time." and then totally forget about it.If you scold yourself, get angry etc, you will just go onto to further program your subconscious for future failure.
You may have developed a self image that sets you up for failure.This self image needs to change.Feeding yourself with postives (affirmations etc) and starving it from negetivity will eventually change your self image if you are diligent. Having said that, change isn't easy.
These are reccomendations from books on the mental game.This is not my own self prescribed therapy. I've been to lazy to(consistently) try them for myself,but when I have, it seems to work. Sorry I can't offer you more, however, studying the mental game is something that I too so despretley need and have only began to work on.
Mechanics and knowledge only take you so far. This game is sooooo MENTAL.Good luck.
RJ
Here's an excellent mental book that I've started to read:
With Winning in Mind, by Lenny Bassham
(Olympic Champion and two time World champion target shooting)
Great little book, that I'm really impressed with.