In addition to the Rules and Etiquette, a number of interpretations of the Rules have been published by the USGA/R and A that prescribe the proper procedure in certain situations where the Rules themselves may not be clear.
The Decisions are numbered based on the Rule or sub-rule being interpreted and the order in which Decisions were published.
When a player has a question, they may ask a rules official who has an actual Decisions Book.
Decisions may be simple clarifications.
For instance, a note in Rule 17-1 says anyone standing near the flagstick is deemed to be attending it.
This is vague, so Decision 17-1/1 states that anyone close enough to touch the flagstick is “standing near” it.
Decisions may also define the proper procedure in exceptional or unforeseen cases.
For instance, Decision 6-6a/4 states when the scorekeeper refuses to sign a card after a dispute about his fellow-competitor’s score is decided by the committee in favor of the fellow-competitor.
There is no penalty; the scorekeeper should not attest to any score he believes incorrect even if he is overruled.
But the score may be attested by another witness, or may be accepted by the committee without being attested.
Decisions may also rule that specific actions, equipment or fixtures used by a player or implemented by the committee or course are legal or illegal;
for instance, most decisions regarding Rule 14-1 define specific actions that are and are not fair swings at the ball, and general decisions on rule 17 define alterations to a flag or attachments to the flagstick that may be made by the course authorities to indicate the relative position of the hole on the green, or aid in distance determination.
These decisions are binding in situations where they apply, as they define the proper implementation of the Rules themselves.
They are not included in most rulebooks, but like the Rules they are available for reference on the USGA website.