How to Challenge a Call
When you feel that your opponent made an incorrect call, it's important to know the rules regarding how to correctly challenge that call. The Code is pretty clear on this:
"Player makes calls on his side of the net. A player calls all shots landing on, or aimed at, his side of the net.
Opponent’s calls questioned. A player may ask his opponent about his call by the query: “Are you sure of your call?” There shall be no further delay or discussion. If the opponent reaffirms that the ball was out, his call shall be accepted. If the opponent acknowledges that he is uncertain, he loses the point."
Furthermore, the challenger is NOT to cross the net to her opponent's side of the court unless invited, nor to call their coach/pro to arbitrate.
Knowing the protocol of challenging a call is important to avoid arguments and maintain an atmosphere of courtesy on the court.
NOTE: Players who consistently make bad line calls from match to match suffer from "tennis anxiety" caused by a fear of losing to players perceived to be of lower skill or ability. It is a defence mechanism used to compensate for their lack of skill. Either that or they simply have poor eyesight, in which case, they should defer the call to their partner or as a last resort, their opponents.