The 90-degree rule states that when your disc contacts an opponent’s disc, it will always rebound at a 90-degree angle, regardless of the angle at which you shoot.
Here we see the different components of a 90-degree shot. The white and black dot represents the exact spot where the shooter’s disc needs to contact the opponent's disc. If successful, the opponent's disc will move forward along the 90-degree line each time.
The tangent line indicates the direction the shooter’s disc will follow after contact with the opponent’s disc. The line crossing the ghost disc indicates the actual direction of the shooter’s disc, going through the middle of the ghost disc. This is the line you need to focus on, as the ghost disc will follow the tangent line’s direction, regardless of the shooting angle.
Download a free cutout template of the 90-degree chart to use on your crokinole board.
https://crokinole.wixsite.com/illustrated-guide
Real-World Application
Let's now see how this rule applies in a real-game scenario.
The ghost disc (G) represents the exact location where the shooter's disc comes in contact with the opponent's disc.
I use the name ghost disk to show the trajectory of the disc you’ve flicked. Here you can clearly see its contact point (the white and black dot) as well as the direction line your disk will travel to its final landing spot.
In the diagrams below we will presume it's your turn to play and there is only one opponent’s disc on the playing surface.
Step One
In step 1 we start by analyzing your opponent’s disc. Decide if you can use one shot to both knock the black disc off the playing surface and land your disc in the twenty-hole. Let’s assume that in this case, you’ve decided this is possible.
Step Two
Try to visualize the tangent guideline as seen in step 2, then determine both the direction your disc will go and that of your opponent's disc. Now you know where to aim your disc. Note, that your aim should be the white and black dot.
Next, imagine the actual path your disc will travel using the line parallel to the tangent line. This is important to remember since the actual tangent line will send your disc directly to peg eight. It’s the line parallel to the tangent line that will send your disc between pegs one and eight.
If you have difficulty imagining the tangent line, use the free PDF cutout available for download on my website. Note that using the PDF tangent line guide is only good for practice sessions. It’s not a good idea to use the guide when playing with a real opponent.
Step Three
Step 3 shows how to position your white disc so it contacts the opponent’s black disc precisely where the tangent line meets the black disc at the white and black dot.
Step Four
Notice in step 4 that the white disc will rebound off the opponent's black disc, travelling along the direction line following the direction of the tangent line to end up in the twenty-hole. With the same shot, the opponent's black disc will follow the 90-degree line off the playing surface.
The great thing about the 90-degree rule is that the rebound will always follow the tangent line regardless of the shooter’s angle, and the opponent’s disc will always move at a 90-degree angle.
While some angles are more challenging than others, the tangent line rule always applies. The force of impact will vary depending on the angle needed, so practice, practice, and then practice some more.
Exception
There is one exception to the 90-degree rule: the hit-and-stick shot. If you hit the opponent’s black disc perfectly square on the white and black dot without any angle, the opponent’s disc will move straight along the 90-degree line as expected, while your disc will stop dead at the point of contact.
A cutout templat of the 90-degre
https://crokinole.wixsite.com/illustrated-guide
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