stun

• definitions
• 90-degree rule

for more information, see Sections 3.03 and 4.02 in The Illustrated Principles of Pool and Billiards
and Disc I of the Video Encyclopedia of Pool Shots

definitions

What does stun mean?

Stun means pure sliding, where there is no topspin or bottom spin. With a stun shot, the CB has no top or bottom spin when it hits the OB. For a straight in stun shot, the CB stops in place and transfers all of its energy to the OB. This is called a stop shot. With any other stun shot, with a cut angle, the CB heads in the tangent-line direction, regardless of the cut angle (see the 90-degree rule). A stun shot is sometimes called a "stop shot at an angle."

With a stun shot, the CB must be struck below center. The bottom spin will wear off (this is called drag) on the way to the OB. The farther the CB is from the OB, the lower and/or faster you need to strike the CB to prevent the CB from losing the bottom spin and starting to developing forward roll before hitting the OB. If the CB has any topspin when it hits the OB, the CB will follow forward. Here's a slow motion video showing how drag works with a stop shot:

• HSV 3.1 - Stop-shot showing loss of bottom spin over distance

Here's an example stun shot:

• NV 4.1 - Stun shot

from Patrick Johnson:

90-degree rule

What is the 90-degree rule ?

The 90-degree rule states that for a stun shot, the CB and OB separate at 90 degrees, regardless of the cut angle (except for a straight-in shot, in which case the CB stops in place). In other words, with a stun shot the CB heads and persists along the tangent line direction, which is perpendicular to the line of centers (the line between the center of the ghost ball and OB). Here are some relevant video demonstrations:

• NV 3.4 - 90° rule with various cut angles
• NV 3.5 - Using your hand to visualize the 90° rule impact and tangent lines
• NV 3.6 - Stop shot
• NV 3.7 - Using the 90° rule to check for and prevent a scratch
• NV 4.1 - Stun shot

Here's a convenient 1-page summary resource page summarizing all of the important points of the 90-degree rule.

Here's a good drill for practicing stun shots: stop/follow/draw drill.

For more info, see: where the CB goes for different cases.