First of all, the reason I ask the following is because, I would think any ball movement is a penalty after address if it was caused by address. However, I see time and time again, pros on TV do it and there does not seem to be an issue when they do so. No mention of it by the commentators, usually. So, what is the proper way to treat the following situation? Penalty or no penalty? I should probably know this since it is so common, but honestly, I'm not really sure? Forgive my ignorance.

Your ball is in thick rough, or any rough for that matter. You address the ball and lightly rest your club down on the rough a little behind the ball. In doing so, the ball does not actually move relative to the grass it is sitting on, however, all the grass around it, including that on which the ball sits, sways/bends from the weight of the club. The ball is not touched by the club and the ball does not change it's position in any way relative to the lie. Technically, it has moved from a point in space of which it once occupied, but so has everything else connected to it.

Is there somewhere in the rules, or rulings where this common situation has been addressed? I have read through rule 18, but there is nothing specific there. That rule states that if a ball is moved it must be replaced, but in this scenario, you can't replace something that hasn't changed position relative to the environment around it. I have seen it happen a number of times on TV with no consequence, so maybe I just need a better understanding of the rule.

I'm sure all you rules experts (bkuehn, Jev, Rulesman, etc.) can answer this one. So, I'm all ears. Straighten me out.

Decision 18/2 addresses this issue. If the player causes the ball to oscillate, but the ball returns to its original position, it is deemed to not have been moved. My interpretation of this is if the ball is sitting in the rough, then moving the rough with one's club will cause the ball to oscillate. In one's backswing, the ball will return to its original position.

If the ball moves with the grass and it is caused by the grounding of the club, one shot penalty and replace the ball to its original position. As DougE pointed out, moving the ball back is almost impossible because the ball really only moved downward a tiny amount as the grass sagged. Still one must try to do so. Jack Nicklaus used to never ground his club in the rough because of concern over the ball moving. If today's pro's are moving the ball when they ground their club, they should be adding a stroke like the rest of us.

"Oscillating" is the wiggling of the ball without the ball changing positions. Bryan K is correct that making the ball oscillate is not a penalty. Oscillating is not the same, however, as a ball settling a bit further into the rough In that instance the ball changes position. Typically one sees oscillation on the green or fairway when one accidently taps the ball lightly and is kind of rocks forward and back without actually leaving its spot after the rocking is done.

The USGA told me once that if one pulled a grass blade and the ball rotated without apparently moving downward or laterally, they would still consider the ball to have moved, resulting in a penalty. So if the ball moves at all, you have a problem.

See the movie the legend of bagger vance.