CROQUET COACHING:  Angle of Rush

When rushing a ball, at what angle will the roqueted ball travel?  If you were to hit the roquet at the dead center of the roqueted ball, then obviously the rush would be in the same direction as the striker ball is traveling; that is, at an angle of zero degrees from the direction of the striker ball.  But what if you roquet off center -- a cut rush?

Let each croquet ball be of radius R.

At the moment that Blue (striker ball) comes into contact with Red (roqueted ball), the direction of travel of Red will be along the line joining the centers of the two balls.

If the direction of travel of Blue was off center of Red by the amount r from the center of Red, then the angle (a) between the direction of travel of Red and Blue can be computed with the formula a = arcsin(r/2R).

For example, if Blue were aimed at the edge of Red, then r = R, and a = arcsin(1/2)= 30 degrees.  That is, the roqueted ball will be rushed at an angle of thirty degrees from the direction of travel of striker ball.

The graph of a as a function of r (expressed as a fraction of R) is almost linear until r is almost equal to 2R.  So if you remember five different cases, you'll be able to extrapolate easily between them.
 
 

Point of Aim (r)	0	R/2	R	3R/2	2R
Angle of Rush (a)	0°	15°	30°	45°	90°

This can be shown more graphically with a yellow rushed ball, and the arrows representing the five cases.

If you keep this image in your mind, you'll be able to tell where to aim at the roqueted ball to get just the angle of rush you want.