All the bickering aside, I think it is reasonable for some people to think there might have been some "theatrics" involved. And to answer the question as to why? and what would he gain by it? Just ask Michelle Wie. You gain an excuse in case you lose. That said...
I was not one that thought he was faking it.
My theory on why he was grimacing more on some shots than others and more often than not on the bad shots...is that the adrenaline rush from a good shot overshadowed the pain. Likewise, on a bad shot, the adrenaline isn't enough to numb the pain. I don't know about any of you, but I've played sports hurt before and the thrill of performing right seems to give you that extra little shot of adrenaline that makes you forget about your injury for a short time and when you screw it up...for some reason you notice the pain more. Maybe that's just me, but I can totally relate to the situation from personal experience on a NON-professional level. After finding out just what all was wrong with Tiger, I think the man is incredible for doing what he did and not just playing well, but winning the US Open.
Feel free to attack me, my opinions or thoughts or to just keep bickering.

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"...I bow to your greater knowledge..." -- Lefty of GRW in response to one of my posts
Winner of three 2007 Golf Rewound Pick Em Contests:
Players Championship, US Open & PGA Championship
Repeat Champion of the 2008 US Open Pick Em Contest