Measurement of hand grip

The correct Racquet is also very important for injury prevention. A grip that is too small often results in the inability to hold onto the racket adequately.5 A grip that is too big often results in constant contraction of the forearm muscles because the player is afraid they will lose their grip.5 Measure from the lower crosswise crease on the palm to the tip of the fourth finger to determine the correct grip size in inches.5,11 If the measurement is between grip sizes, a smaller size is recommended because grip tape can be wrapped easily around the grip to increase the size.5 An oversized racket with a larger sweet spot provides more stability, less twisting and reduced arm vibration.5 A stiffer racket frame also reduces vibration and dampens vibration more quickly.5 Cushioned grip tape increases racket dampening by up to 100%.5 Lowering string tension creates a trampoline effect which absorbs some of the shock from ball impact.5,9 A tether will keep the racquetball racquet from flying out of your sweaty grip and possibly hitting your opponent or yourself.2
Illustration courtesy of Reference 11.
With a proper fitting grip, you should be able to fit the index finger of your non-hitting hand between the palm and ring finger as shown.11