Definition of western grip in US English:

western grip

noun

Tennis
  • A manner of gripping the racket in which (for a right-handed player) the heel of the hand is in contact with the bottom of the handle and the bottom knuckle of the index finger touches the bevel immediately counterclockwise from it, typically used to generate heavy topspin.

    ‘a western grip on the forehand gives him fewer options on low, short balls near the net’

Origin

1920s: so named because it was originally considered characteristic of tennis players from the West Coast of the US.