It was an innocent mistake that caused a flurry of confusion.

Stamford Bridge, July 18 this year. Maurizio Sarri is being presented to the media as Chelsea's new manager. He is asked for his thoughts on the squad that he has inherited from Antonio Conte, and the interpreter who translates his answer from Italian into English reveals that the former Napoli coach is eager to add "a pinch of quality" to his central defence.

The journalists in the press conference room beneath Stamford Bridge's East Stand post the remark on their social media accounts, and Twitter is instantly abuzz. What can he mean? Is this curtains for Gary Cahill? Cheerio to Andreas Christensen? Hasta la vista, David Luiz?

Ultimately, it was none of those things. Sarri had been talking about the centre of midfield rather than the centre of defence, and the interpreter had simply used the wrong word. No sooner had the press conference finished than Chelsea's media team had issued a clarification on the matter. Their central midfielders might need to watch their step, but their centre-backs were safe.

The episode demonstrated the fundamental importance of language in football and highlighted the pivotal role played by interpreters. The men and women who repackage the words of the sport's great and good walk a tightrope every time they sit down at a press conference's top table: Do the job properly, and nobody notices; get even the tiniest detail wrong, and all hell can break loose.

"To me, a good interpreter is like a good referee or a good commentator: You don't really notice they're there," says Patrick Kendrick, a football interpreter and broadcaster who has interpreted for figures including Sarri, Conte, Jose Mourinho and Mauricio Pochettino.

For those in the trade, preparation for an interpreting assignment begins well before the event itself. Interpreters must be familiar with any topic that might arise in a press conference or interview, which means intimately acquainting themselves with whichever teams that will be spoken about—injuries, playing tactics, recent news—as well as any names liable to be mentioned.

"Names are always the biggest difficulty," says Kendrick, who works in French, Italian and English. "You don't want to get them wrong."

Interpreters use YouTube videos of those they will be interpreting to familiarise themselves with their accent, the pace at which they speak, phrases they tend to use and any vocal tics. The note-taking that forms an essential part of interpreting might also be rehearsed.

"Before I do a job, I'll generally sit down and practise all the little abbreviations I might use," says Rob Hunt, who has worked with Premier League players such as Chelsea midfielder Jorginho and Tottenham pair Davinson Sanchez and Erik Lamela.

"Depending on the player, I'll come up with something for their club, and it's usually just initials for the different players. Over the years I've developed my own glossaries of [foreign] terms that come up. I'll have a look at them to refamiliarise myself with the language that I'm doing."

When working at a match, an interpreter must have a clear understanding of any contentious incidents likely to be picked over with forensic detail after the game.

The interpreter needs to be on hand when the managers arrive for their press conferences, and Kendrick says that the job involves a lot of "awkward lurking" in the vicinity of the top table. When the manager enters the room, a hush descends and the television cameras begin to roll. Then, it's showtime.

"If you get a 'hello' and a handshake from the manager before, you can count yourself lucky," says Hunt. "Then you're kind of thrown into the bearpit."

There are two types of interpretation: consecutive, when the interpreter waits for the manager to finish speaking and then interprets what they have said, and simultaneous, when an interpreter in a booth translates as the subject is talking, with the interpretation relayed to those in the room via electronic headsets.

Everything that is said into must be translated and then delivered in a manner that captures every nuance of the speech. And all without the slightest hesitation.

As a general rule, managers are more challenging subjects than players, given that they are more likely to use both precise technical language and elaborate metaphors. Their changeable moods represent an occupational hazard, not least when they have just watched their team lose and must sit silently while their answers are interpreted.

"They just want to do the press conference quickly and get home, but you have to interpret," says Kendrick. "I've literally heard sighs from some coaches."

Occasionally an interpreter will know the words leaving their mouth will appear on the following day's newspaper back pages. Marc Joss was providing interpretation at a Europa League qualifier between West Ham United and Andorran minnows Lusitans in July 2015 when visiting coach Xavi Roura began to lambast freshly appointed Hammers manager Slaven Bilic for having watched the game from the stands.

"He came in, sat down and started ranting in Spanish about how Slaven Bilic not being in the dugout was a massive lack of respect," says Joss. "I was sitting there, looking at him almost in disbelief at what he was saying, and then I realised that I had to say it all in English."

Joss and Hunt both cite Diego Costa as a challenging person to work with due to his heavily accented blend of Portuguese and Spanish. Phil Dickinson, who is one of Britain's most experienced and well respected football interpreters, had similar problems with former Arsenal forward Jose Antonio Reyes.

"Reyes was talking about place names and the local Madonna who he worshipped, but you just couldn't understand it," Dickinson says. "I had to ask his agent what he'd been talking about."

One of the perks of the job is the insight it can afford interpreters into the lives of famous players and the inner workings of leading football clubs.

Dickinson, who set up his own football interpreting firm, Premier Language Solutions, in 2001, was employed by Wigan Athletic to provide translations for Ecuadorian winger Antonio Valencia following his arrival in England in 2006. The role involved sitting beside the future Manchester United captain in the changing room and whispering tactical instructions translated from the words of his manager, Paul Jewell, and team-mates into his ear.

"There'd be Antonio on one side, then [Emile] Heskey, then Kevin Kilbane," Dickinson recalls.

"[Leighton] Baines was really friendly with Antonio. He was quite insightful tactically and he'd always have some advice at half-time. It was a great atmosphere in that dressing room. You're an interpreter, but you're almost part of the team in a small way."

Joss worked closely with Dimitri Payet during the France international's time at West Ham. After learning that Joss was an Arsenal fan, Payet presented him with a shirt worn by Laurent Koscielny in one of the last matches at Upton Park.

Hunt found himself secretly rooting for Tiemoue Bakayoko last season after developing a rapport with the French midfielder following his arrival at Chelsea from Monaco.

"I remember crossing my fingers that his form would turn around, but he never quite managed it," he says.

Paths into football interpreting vary. Some will have done a master's degree in interpretation, whereas others will have no formal training. Dickinson, who has over 30 years' experience, previously worked as a holiday rep and an English teacher in Spain. Joss' big break was a chance encounter with Spanish football journalist Guillem Balague at Luton Airport in 2013 that led to him helping to translate Balague's authorised biography of Lionel Messi into English.

Within the industry, there is an expectation that European governing body UEFA will begin to push for more simultaneous interpretation at events such as Champions League matches, rather than relying on the slower process of consecutive interpretation. As top-level football becomes ever more professionalised, organisations such as UEFA and FIFA could also bring themselves into line with institutions such as the United Nations and the European Union by obliging its interpreters to pass formal tests.

For now, the doors to football interpreting are open to anyone with a love of languages, a detailed knowledge of the game and an ability to think and speak in multiple dialects in front of a room of unforgiving journalists and a potential TV audience of millions. Simple, no?