I'm writing this article because recently it has come to my attention that the "bad line call" is in fact a part of tennis. Everyone who has ever played tennis regularly has missed line calls at some point in time...
Both on the ones that were actually out (whether on a serve or on the sideline/baseline) but we played anyway AND when we made inaccurate out calls on balls that were actually in. But we made in good faith with our less than "Shot-Spot-perfect" eyes.
Yes. You are, I am, we all are H-U-M-A-N. It happens....A lot actually!
Nobody is perfect, nor faultless (Players nor Officials)
Just look at this: 2013 Australian Open Challenge Statistics compiled after this year's Grand Slam tournament. At the Top Professional Level of tennis in the ATP and WTA, the players themselves, were wrong more than 2/3 of the time (about 70% of the time, the challenger was incorrect).
Remember, there are only a very limited in the amount of challenges available per set, so you can assume that they challenged because they genuinely felt unsatisfied with the ruling made on the court.
What is maybe more interesting is how often the Officials were wrong. Even when you have officials on every line and highly-paid umpires, they were actually "Caught" by Shot-Spot being wrong about 25% of the time, and those points had to be overturned or replayed. Just for the record, that was (at least) 189 times during that tournament alone where the officials were wrong, to be precise, according to the Australian Open website.
So that means that even these are paid and trained officials during the average match are missing about 1 or 2 calls per match at a Grand Slam. And yes, this is when those players are actually playing for millions of dollars AND Wimbledon is on the line =)
Therefore in amateur matches and local pick-up games, you can expect to have a few missed calls (both in the caller's favor and sometimes a mistake in NOT calling and against their favor). If we make all calls in good faith, then for the most part, it should even out in the end. Or at least not effect the final outcome of a match...
What we do and how we react to this is the important part.
You cannot immediately over-react and assume your opponent is a cheater. Getting mad or upset or rattled about one bad call is a mental weakness.
You should assume they made a mistake and not a deliberate one. If it happens continually, then go ask for a line judge. It helps free up both players to hit the ball and not worry as much on making every call perfectly.
The USTA code of tennis says you can challenge or ask for a confirmation on the call from your opponent, but without an official there watching it is your Opponent who has the Right to make the call on his/her side of the court then you should accept it and move on. Important: *If you didn't see the ball land and space between the line and the ball, you should always assume it was in.*