Players may call Lines on Opponents' Court to player's disadvantage.

Revised 13.D.1.b. Players make all line calls, non-volley zone fault calls, and service foot fault calls on their end of the court. Players may call lines on the opponents's end of the court to the player's disadvantage.

Polls have shown roughly half of players believe they should be able to make their own unsolicited line calls of OUT on balls they have struck to the opponents' court. Current rules do not directly address this, the nearest rules being 13.D.1.a., which deals with players calling faults against themselves or partners; and 6.C.11. which allows overrule of "IN rulings", a bit problematic since the rules do not define a ball considered IN as equal to an "IN call" or "IN ruling". With a specific rule allowing far court OUT calls, 6.C.11. can return to being purely for overrule of adjudicated rulings from refs, partners, or opponents.

Section 6 on Line Calls is comprehensive, nearly 1000 words. Making calls on the opponents' court should have proper treatment that governs the practice and removes any doubt.  Similar language should be introduced into Section 6 with a rule revision submission.