5.4 The Return of Service and Rally Play (WSF Rules of Squash, Rules 9 & 10)

A player may also play the ball onto a side wall or the back wall first, provided the ball then strikes the front wall above the tin and below the out line (these are called "boast" or "angle" shots).

Source: Rule 9.1, Rule 10, Rule 10.1, Rule 10.2, Rule 10.3, Rule 10.4, Rule 10.5, Rule 10.6, Rule 12, Rule 12.1, Rule 12.4, Rule 12.6, Rule 13, Rule 13.1.1, Rule 13.1.2, Rule 13.1.3, Rule 13.1.4, Rule 6, Rule 6.1, Rule 6.2

Send this to your friend — argument over.