# How Do I Stop Scratching On This Shot?

#### tim913

##### AzB Silver Member
Silver Member
A lot of good advice but if you’re having trouble move the CB closer to OB, keeping the same angle, and practice from there. As your confidence grows move the CB back a half diamond at a time till you’re where you’re at now. After you’re making most of them you’re going to have to learn to not only make it but move the CB to your next shot

#### ChrisinNC

##### AzB Silver Member
Silver Member
The Semi-Circle of Death is the half circle drawn from corner pocket to corner pocket passing through the spot. Straight lines to both corner pockets from any point on that semi-circle form a 90-degree angle. That means pocketing an OB that's on that semi-circle (including a ball on the spot) into either corner pocket with a stun hit (so the CB caroms straight along the 90-degree "tangent line") will scratch the CB in the other corner pocket.

pj
chgo
I would love to see a diagram of this semi circle of death, to use for instructional purposes. Anyone know where I might find one? - thanks

#### Patrick Johnson

##### Fish of the Day
Silver Member
I would love to see a diagram of this semi circle of death, to use for instructional purposes. Anyone know where I might find one? - thanks
The first drawing shows the Semicircle of Death (dashed line) for the shot posted above. The solid lines are examples showing the right angles formed at various places on the semicircle connected to both pockets.

The second drawing shows more Semicircles of Death in several places on the table - wherever a semicircle can connect two pockets.

pj
chgo

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#### ChrisinNC

##### AzB Silver Member
Silver Member
The first drawing shows the Semicircle of Death (dashed line) for the shot posted above. The solid lines are examples showing the right angles formed at various places on the semicircle connected to both pockets.

The second drawing shows more Semicircles of Death in several places on the table - wherever a semicircle can connect two pockets.

pj
chgo

View attachment 601597
View attachment 601598
Thanks! In the OP‘s original diagram, the 8-ball appeared to be located a few inches below the foot spot, which is even more reason it would be easy to avoid the scratch.

#### Scott Lee

##### AzB Silver Member
Silver Member
I can make this shot 8 out of 10 times, unfortunately I scratch about the same amount of times. How do I not pocked the cue ball on this shot? View attachment 601336
Quit shooting so hard. Otherwise you will scratch every time. Roll the CB and cut the 8 in.

Scott Lee

#### PoolPlayer4

##### AzB Silver Member
Silver Member
The first drawing shows the Semicircle of Death (dashed line) for the shot posted above. The solid lines are examples showing the right angles formed at various places on the semicircle connected to both pockets.

The second drawing shows more Semicircles of Death in several places on the table - wherever a semicircle can connect two pockets.

pj
chgo

View attachment 601597
View attachment 601598
Are there any resources that explain how this is put to use?

Silver Member

#### PoolPlayer4

##### AzB Silver Member
Silver Member
If you know what a tangent line is and how to use it to predict/control the direction the CB goes after contact, then you know all there is to know about it. As usual, I recommend Dr. Dave's info on it: https://billiards.colostate.edu/faq/stun/90-degree-rule/

pj
chgo
I have a good understanding of the tangent line and using it to predict cue ball direction. Execution is another matter. Just wondering if the circles had some practical application.

For what it's worth, I can scratch from just about anywhere on the table!

#### Patrick Johnson

##### Fish of the Day
Silver Member
Just wondering if the circles had some practical application.
None that I know of, other than being able to predict the scratch - but if you know your tangent line stuff you already know that for every shot, including the ones on these lines.

pj
chgo

#### ctyhntr

##### RIP Kelly
Silver Member
The Semi-Circle of Death is the half circle drawn from corner pocket to corner pocket passing through the spot. Straight lines to both corner pockets from any point on that semi-circle form a 90-degree angle. That means pocketing an OB that's on that semi-circle (including a ball on the spot) into either corner pocket with a stun hit (so the CB caroms straight along the 90-degree "tangent line") will scratch the CB in the other corner pocket.

pj
chgo

Dollar bill is an easy and handy rule to check the tangent line, as it has 90 degree angles.

#### Bob Jewett

##### AZB Osmium Member
Staff member
Gold Member
Silver Member
Dollar bill is an easy and handy rule to check the tangent line, as it has 90 degree angles.
I think one of the most important skills for a player to acquire to get past "OK intermediate" level is to learn to judge tangents and right angles by eye. And I know at least one "pro" player who would call a foul if you got a "measuring device" out of your wallet.

#### Banger

##### AzB Silver Member
Silver Member
My goodness, how could any functioning adult not know what a 90 degree angle looks like? And I see players (even pros) using measuring devices all the time....they use their cue stick to determine angles off the rail, particularly on bank shots.

#### ChrisinNC

##### AzB Silver Member
Silver Member
My goodness, how could any functioning adult not know what a 90 degree angle looks like? And I see players (even pros) using measuring devices all the time....they use their cue stick to determine angles off the rail, particularly on bank shots.
Your cue stick is the only thing that by the rules you are allowed to use as a measuring / alignment device, as long as you don’t let loose of it.

#### Bob Jewett

##### AZB Osmium Member
Staff member
Gold Member
Silver Member
My goodness, how could any functioning adult not know what a 90 degree angle looks like? ...
Many people escape from school rather than graduate from it. I know an instructor who felt it necessary to build a right angle from PVC pipe so his students could see a right angle.

If a shot is aligned with the sides of the table (NSEW), most people will get the "right" answer. If the shot is 24 degrees off axis, the perpendicular for a large fraction of students ends up in very strange places. This is a large problem when learning to play position.

#### justnum

##### Redhawk PI
Silver Member
My goodness, how could any functioning adult not know what a 90 degree angle looks like? And I see players (even pros) using measuring devices all the time....they use their cue stick to determine angles off the rail, particularly on bank shots.
future cue sticks will have mininprocessors that can use an AI to hypothesize percentages for each shot.

I can post a demo in a few months.

#### Banger

##### AzB Silver Member
Silver Member
Your cue stick is the only thing that by the rules you are allowed to use as a measuring / alignment device, as long as you don’t let loose of it.
Well, it's OK with me. They can use a dollar bill, as far as I'm concerned, as long as they do it in a timely manor.

#### JC

##### Coos Cues
Gold Member
future cue sticks will have mininprocessors that can use an AI to hypothesize percentages for each shot.

I can post a demo in a few months.

#### Banger

##### AzB Silver Member
Silver Member
Many people escape from school rather than graduate from it.
You can't escape from the world. 90 degree angles are everywhere. We grow up looking at 90 degree angles. A piece of paper, the corner of a book, a computer screen, cell phones, the doors in most houses, the wall in most houses, a dollar bill. All have 90 degree angles on the corners.

I know an instructor who felt it necessary to build a right angle from PVC pipe so his students could see a right angle.
It must be mighty discouraging at times, to be an instructor.