A jar is when you hit the wall with the bumper hard enough to either shake the table, or hard enough to influence the movement or position of the ball.
Jars are most often called if someone is in position or attempting to retrieve a ball. If someone already has possession of the ball, and you (as not having possession of the ball) move hard enough to influence movement on the ball, a reset is called instead.
In your case, you would have to hit the wall with the bumper pretty damn hard for a jar to be called on you, wall or brush pass. The most prominent situation for a jar to be called on you would be like this:
- You brush down
- Your opponent is in the way of the brush pass
- As the ball comes close to his man (or even hits his man), you hit the wall hard
That would be a jar.