The Italian rider was excluded from the Tour after the race jury reviewed footage of the incident following the stage. The images show Moscon turning and aiming a blow at Gesbert, who stayed upright on his bike.
This is the first year in which the Tour has had a video commissaire, who observes proceedings on television monitors in a truck at the finish rather than in a car or motorbike within the race.
News of Moscon’s expulsion was formally confirmed when the official stage results began to be distributed shortly after 7.30 Sunday evening.
The commissaires excluded Moscon, citing article 12.1040.30.1 of the UCI regulations, which covers “acts of violence among riders” and allows for disqualification in the event of “particular serious aggression.”
Team Sky manager Dave Brailsford and directeur sportif Nicolas Portal visited the technical zone at the finish line after the stage to review footage with the commissaires and plea Moscon's case.
“The rider pleaded his case through his directeurs sportifs who were heard by the jury of commissaires,” read the statement from the race jury.
The commissaires, led by Juan Martin Sanz of Spain, declined to comment on the matter to reporters gathered in the race permanence in Carcassonne on Sunday evening.
In a statement, Team Sky said: "We support and accept the decision by the race organisers to exclude Gianni Moscon from the Tour de France. Gianni is desperately disappointed in his behaviour and knows that he has let himself, the Team and the race down. We will address this incident with Gianni once the Tour is complete and decide then if any further action should be taken."
Fortuneo-Samsic previously described the incident in a post on social media: “800 metres after the start of the 15th stage, Elie Gesbert received a punch from Gianni Moscon. After reviewing the images, the jury of commissiares decided to excluded the Sky rider from the Tour de France.”
The incident is the latest addition to the 24-year-old Moscon's already lengthy rap sheet of distasteful behaviour. He was last year accused of deliberately causing Sebastien Reichenbach (FDJ) to crash during the Tre Valli Varesine, but the UCI disciplinary committee dropped the case in June, citing a lack of evidence due to the absence of video footage.
Reichenbach suffered a fractured elbow and hip in the crash, and the Swiss rider believed Moscon deliberately caused the crash in retribution for his part in highlighting how the Team Sky rider had racially abused Kevin Reza at the 2017 Tour de Romandie.
Moscon was side-lined from racing for six weeks by his Sky team after he admitted to racially abusing Reza, though the squad allowed him to complete the Tour de Romandie. The UCI, however, declined to take any action against the Italian rider for the racist incident.
Following Moscon’s racial abuse of Reza in 2017, Team Sky said: “Gianni knows that there is no excuse for his behaviour and that any repeat will result in termination of his contract.”
In September of last year, Moscon was disqualified from the World Championships road race when video emerged of him taking a tow from the Italian team car after he was caught up in a crash on the penultimate lap.
Moscon was making his Tour de France debut, and his Sky team currently holds first and second in the overall standings, with Geraint Thomas in yellow ahead of Chris Froome.