There has been much discussion about this and long putters. Effective on the next cycle, January 1, 2016, The Rules of Golf will add a new Rule 14-1B to address "Anchoring a club" to the body. Note that club length is not addressed and the length of a putter can remain, it just cannot be anchored to the body.
Here is the 32 page explanation that addresses ALL concerns and questions from the R&A. I hope you find it useful and it answers your questions.http://www.randa.org/en/RandA/~/media/R ... ation.ashx
In adopting Rule 14-1b,The R&A and the USGA have concluded that freely swinging the entire club is integral to maintaining the traditions of the game and preserving golf as an enjoyable game of skill and challenge.The essence of the traditional method of golf stroke involves the player swinging the club with both the club and the gripping hands being held away from the body. The player’s challenge is to direct and control the movement of the entire club in making the stroke.
To reiterate, the main thrust of Rule 14-1b is to prohibit direct anchoring of the club, where the club or a gripping hand is intentionally held against the body during the stroke.To illustrate this, under the Rule a player may no longer hold a long putter against his or her chest while the stroke is made. but we also do not want the player to be able simply to move the gripping hand off the chest while continuing to hold the forearm against the body during the stroke, because the club would still be effectively anchored. Accordingly, Rule 14-1b provides that a player may not make a stroke using an anchor point, which exists when two things are true: (1) the player intentionally holds a forearm against the body; and (2) he or she grips the club so that the gripping hands are separated and work independently from one another (i.e. the top hand effectively secures the club in place as if attached to the body, while the bottom hand is held down the shaft to swing the lower portion of the club around the stable point of attachment).
That is the narrow issue addressed by the prohibition on using an anchor point during a stroke.There is no general ban on contact between the player’s forearms and body. Other than when an anchor point exists, a player may intentionally hold one or both forearms against the body in making a stroke. Specifically, that means that anyone putting with his or her hands together in gripping the club may rest the forearms against the body in any manner without penalty.The “anchor point” provision precludes only a very specific type of stroke in which a forearm is intentionally held against the body as an indirect means of anchoring the club.
This gives a general overview of the Rule and reasons for the change.