Here's a question we get from time to time:
"Following my first putt on the green, my ball rolled into a green-side bunker. Can I declare my ball 'unplayable,' and go back to the last spot where I last hit it to re-play the shot?"

The short answer: Yes.

It's counterintuitive, becase declaring a ball unplayable when, in fact, the ball is eminently playable seems counter to the basic golf principle of "play it as it lies."

In the scenario described above, the golfer would remove the ball from the bunker, assess himself a 1-stroke penalty, place the ball at the spot of the original putt and try again. You never, ever see pros doing something like this because pros are unwilling to take the penalty. A golfer who is terrified of sand (pros consider sand shots among the easier shots in golf) might, however, think that 1-stroke penalty is worth it to get out of the sand.

Fact is, a golfer can declare any ball unplayable, at any time, for any reason, and anywhere on the course other than in a water hazard. The penalty is one stroke with three options for how to proceed.

In the rulebook, it's Rule 28, Ball Unplayable, and it's as straightforward as can be:

"The player may declare his ball unplayable at any place on the course except when the ball is in a water hazard. The player is the sole judge as to whether his ball is unplayable."

After taking a 1-stroke penalty, the three options for proceeding are to return to the spot of the previous stroke and play again; or drop within two club lengths, not nearer the hole; or drop behind the spot, going back as far as you want, keeping the original spot between the hole and the spot where the ball is dropped.

If you declare a ball in a bunker unplayable and use the second or third option (taking a drop), you must drop in the bunker.

For a little more explanation, read Rule 28. It's every bit as clear as it sounds, even if that doesn't sound quite right.

...Tom gave unsolicited advice to
his friend Bill as he prepared to hit his chip shot
on the same hole. What should be the ruling here?

ANSWER: It doesn't matter that Tom had finished his
round, other competitors were still playing the hole.

Rule 8-1 stipulates that a player may not give advice
to anyone playing the course other than his partner. Even telling him to take his time

Tom got himself a two stroke penalty.

Instead of dropping within two club-lengths, he
determines where he will have the clearest shot
to the green and drops in line with the hole
approximately 50 yards behind where his unplayable
ball rested.

What is the ruling?

ANSWER 91: There is no need for a ruling in this
case. Rule 28(b) provides an option to drop a ball
behind the point where the ball lay, keeping that
point directly behind the hole and the spot on
which the ball is dropped, with no limit to how
far behind that point the ball may be dropped.

While playing a match, Player A hits
a 30-foot, left to right breaking putt to within
two feet of the hole.

Player B says, "That's a good one."

Player A, believing that Player B has conceded
the putt, picks up his ball.

Player B then says, "I didn't concede the putt."

What is the ruling in this case?

ANSWER: In the case of this misunderstanding,
Rule 1-4 would come into play. It states that
any point in dispute must be resolved in accordance
with equity.

It would appear that the fair thing to do in this
case would be for Player A to replace his ball
without penalty.

.....Tom looks at his lie and the ball, then
removes a blade of grass from the side of the ball.

Was he allowed to remove the blade of grass?

ANSWER 77: According to the Definition anything
adhering to the ball is not a Loose Impediment.
As such, removing the blade of grass would be
akin to cleaning the ball, which, in this instance,
is not allowable under Rule 21.

Tom can remove the blade of grass, but under a
penalty of one stroke

As you can see the WhatsTheScore team guessed 28 and was closest (see comments below), but we are willing to share the prize with our members!

2nd place was Steve P. Taylor from Oldham Golf Club with a prediction of 37.

Other who were very close (but no cigar) were Stephen Grouwstra and Maurice Lynch

... Player A has already played his shot and his ball has come to rest up ahead. Player B takes his stroke and when his ball hits the ground, it rolls right into Player A's ball. Both balls careen away.
What's the ruling?

Depends on where the balls where before the fateful shot was struck: were both balls already on the green, or were neither or just one of the balls on the green?

Scenario 1: Neither Ball, or Just one Ball, on the Green
This could mean the shot in question was a tee shot, or an approach played into a green, or any other scenario other than when both balls were on the green prior to making the stroke.

For example, your partner hits a tee shot, then you hit yours, and your ball hits your partner's ball in the fairway. Or your partner is on the green, you hit an approach shot, and your ball hits your partner's on the green.

This is covered in Rule 18-5, Ball at Rest Moved by Another Ball. There is no penalty to either player as long as this procedure is followed: The person whose shot struck the ball at rest plays his ball as it lies; the person whose ball was moved returns the ball to its original position.

Failure to replace the ball that was moved to its original spot; or moving the ball that did the striking (rather than playing it as it lies) results in loss of hole in match play or a 2-stroke penalty in stroke play.

Scenario 2: Both Balls on Putting Green
"Both balls on putting green" means on the putting green prior to the stroke in question.

The ruling here is covered in Rule 19-5a.

From the green, Player A hits his putt, but the ball strikes the ball of Player B, who was also on the green. In match play there is no penalty. In stroke play, it's a 2-stroke penalty to the player whose ball was in motion when the balls collided.

Repeat: It's not a penalty against the player whose ball was at rest; the penalty is against the player who struck the putt.

The player whose ball was at rest replaces it to its original position; the player whose ball was in motion plays it as it lies