Two teams are playing interclub, on one of team A’s shots, team B says
“I can’t be sure if it was out, so it’s your point”.

Later, on one of team B’s shots, team A says
“I’m not sure about that ball let’s play a let”.

In the two identical situations there are two very different outcomes, this is why we need a code of conduct.

Rules

Benefit of the doubt

When playing without umpires a player must abide by the unwritten law that says any doubt must be resolved in favour of the opponent.
This means that any ball that cannot be called out with surety is presumed to be good and play continues.
No point should be replayed because a player is unsure whether the ball was in or out.

Spectator

In making a line call a player should not enlist the aid of a spectator.

• the spectator has no part in the match.
• they may not be in a position to see the ball correctly.
• they may be prejudiced.
• they may be totally unqualified.

Calls

It is both the obligation and prerogative of a player to call all shots landing on, or aimed at, their side of the net; to help the opponent make calls when the opponent requests it, and to call against themselves any ball that they see out on the opponent’s side of the net (with the exception of the first serve).

All players being human will make the odd mistaken call. They should however do everything they can to minimise these mistakes. In accordance with the law of parallax, the opinion of a player looking down the line is more likely to be accurate than that of a player looking across the line. So the receiver should call the mid-line and tramline, and the non-receiver should call the service line.

Instantaneous calling

Any call of “out”, “let” or “fault” must be made instantaneously, otherwise the ball is considered good and is still in play. In this connotation instantaneously means that the call is made before either an opponent has hit the return or the return has gone out of play. Most importantly a ball is not out until it is called out.

The requirement for an instantaneous call will eliminate the 2-chance option that some players practice. To illustrate this – A is advancing to the net for an easy put away when she sees a ball from an adjoining court rolling towards her. She continues her advance and hits the shot, only to have her supposed easy put away fly out the back. A then makes a claim for a let, which is not valid. A needed to stop when she first saw the ball. When she went for the ball she forfeited her right to a let. She took her chance to win or lose and is not entitled to a second chance.

Another situation eliminated by the instantaneous call requirement is that in which a player returns the ball, at the same time yelling “I don’t know!” This sort of constitutes a puzzle which should not be thrown at any opponent.

In living up to the instantaneous call requirement it is almost certain that there will be out balls that are played. On a fast service for example, sometimes the ball will be moving so fast that the receiver has hit the ball and it has gone into play before an out call can be made. In such cases, the receiver is considered as having taken her chances and is entitled to one only, whether she made a put away or an error.

Serving

If a server or her partner think the serve was out and fail to return the opponents return of serve they lose the point.

"I didn't see the ball"

A player cannot claim a let on the basis that they did not see a ball land. If they could then all they would need to do as you line up a winner is close their eyes! If you don’t see it bounce outside then it is presumed good.

Partners disagree about a call

When one partner calls the ball out and the other good, the doubt that has been established means the ball must be considered to have been good.

The reluctance of some doubles players to overrule their partner is secondary to the importance of not letting your opponents suffer from a bad call.

Service calls

The partner of the receiver should generally call the service line. The receiver should call the centre and sidelines.

Replays

Normally asking for a replay of a point is a sign of weakness and of failure to exercise line-calling responsibilities and should occur only on rare occasions such as:
Your opponent’s ball (serve or other) appears out and you call so, but return the ball to the oppositions side of the court. You then realise the ball was in, and your call stopped play. As you returned the ball, a let is authorised otherwise the point would have been your opponents.

Lets

A let can be called for a disturbance on either side of the net. If player A sees a ball roll onto or behind the court on player X’s side then player A or X can call a let.
If player A holds two balls in one hand to serve and having served her first serve in, drops the ball behind her, the opposition are entitled to call a let.
When you are hindered attempting to return a shot that you could not have returned even had there been no hindrance a let is not authorised.
A request for a let does not mean that the let is automatically granted.
E.g. A request for a let because you tripped over your own hat should not be granted.

Once a call is made

Once an out, let or fault call is made play stops straight away regardless of what happens afterwards.

Housekeeping

Each player is responsible for housekeeping on their side of the net. If they do not remove stray balls (such as after a fault) or other objects, they cannot then claim a let for it later in the point.

Service calls

Returning a first serve that is obviously out to catch the opponent off guard is cheating. At the same time if the receiver, in good faith gives the server the benefit of the doubt, and returns an out ball, the server is not entitled to refuse the benefit of the doubt and ask for a let on the basis that since she saw it out the return caught her by surprise.

Service lets

When the server causes a delay between 1st and 2nd serves they only have one serve.
When the receiver causes the delay, the server has two serves.
When the delay is caused by outside interference (e.g. a ball comes onto the court from another court) the length of delay will determine if a let is authorised.

Double bounce, hitting the net etc

Calls involving a ball touching a player, a player touching the net, a player invading her opponents court, hitting an opponents return before it has passed the net, and a double bounce can be very difficult to make. In all these situations the player involved should make the call.

Receivers not ready

The receiver should make no attempt to return a serve when she is not ready if she wants to maintain valid her right to a let.
On the other hand the server is protected from the '2-chances' for the receiver under the same rule. This rule states that if the receiver makes an attempt to return the serve she is presumed to have been ready-reflex return excepted.

Scoring disputes

In any argument about facts it should be remembered that the position of both sides has equal weight. If the score cannot be agreed, then play should resume from the last score that there is agreement for.

Calling the score

To eliminate arguments about the score the server should announce the game score prior to commencing the service game and the point’s score prior to serving each point.

Foot faults

Foot faults cannot be called in un-umpired matches.

Etiquette

• All balls on your side of the net are your responsibility, to pick up and where appropriate return directly to the server. 
• The receiver should not return the first serve if it is an obvious fault.
• Do not enlist the aid of spectators in making line calls or other decisions.
• Wait until a point is over before walking behind a court where a match is in progress. 
• Do not stall, sulk, complain or practise gamesmanship.
• All calls should be verbal and clearly audible to the opponent, followed by a signal if necessary.
• Mobile phones must be turned off or on silent mode until ALL matches are completed. This applies to spectators as well as players.