They are six young Italians dressed as carrots who are at the French Open in a colourful attempt to inspire Sinner to victory.
From Revello, a small town in Piedmont, they have travelled to Paris, Wimbledon, New York and Melbourne.
"It's crazy and incredible," agree Gianluca Bertorello and Enrico Ponsi, two of the six "Carota Boys", all aged between 25 and 30.
Football and tennis fans, they feel a common connection with the beanpole Sinner who is "a young, simple guy, who like us comes from a small town".
"It all started as a joke. Just a year ago, we decided to have a weekend in Rome to attend the Italian Open," Gianluca told AFP on the sidelines of the recent Rome Open.
"As we wanted to do something different, we dressed as carrots, we had tickets for just one day of the tournament and we were lucky enough that Jannik played that day and won his match," adds Enrico.
Sinner, then eighth in the world rankings, defeated Australia's Thanasi Kokkinakis in that match.
"We encouraged him a lot, we had our costumes and Italian flags, it created a nice atmosphere. But after the match, it became completely crazy: everyone wanted to take photos of us, there were lots of articles about us, mentions on social networks. Our whole story started from there," explained Enrico.
He was keen to add that the carrots are "not a reference to Jannik's red hair".
"It's because we found it amusing and incredible that a player of his level would eat a carrot at a change of ends during the Vienna tournament in 2019," he said.
Back home, the "Carota Boys" were contacted by coffee company Lavazza, one of Sinner's sponsors.
They took them to Roland Garros and trips to Wimbledon, the US Open and the end-of-season ATP Finals in Turin quickly followed.
At the start of 2024, they were on hand to see Sinner win the Australian Open, his first Grand Slam title which ended a 47-year drought for Italian men's tennis.
They also ended up meeting their idol who the described as "someone quiet, nice".
"We have a WhatsApp group with him where we exchange messages - some of us played tennis with him," said Gianluca who even dresses in orange when he's not wearing his carrot costume.
As 22-year-old Sinner, who can replace Novak Djokovic as world number one at the French Open, has climbed the rankings, the "Carota Boys" have seen their popularity soar.
On Instagram, they have 135,000 followers, are represented by two public relations companies and have launched merchandise such as orange t-shirts and caps. They have even published a book.
"This allows us to finance our trips, because it is expensive and is starting to take up a lot of our time," said Enrico who, like the five other members of the group, is single and self-employed.
In his case, he works in the wholesale meat trade.
"Djokovic, Nadal, Alcaraz, they say hello to us," said Enrico.
"Our dream is that Jannik wins all the important titles, and that all the stadiums where he plays in the world have orange stands," he added.
