September 9, 1977. Forest Hills, New York: US Open semifinal.

Jimmy Connors defeats Corrado Barazzutti 7-5, 6-3, 7-5.

It could have been considered routine business for the then four-time Slam champion ‘Jimbo’ Connors, yet the 1977 US Open semifinal turned out to be anything but an easy fight. It was marked, moreover, by one of the most disgraceful and at the same time iconic episodes in the history of modern tennis: an act of unsportsmanlike conduct worthy of the rebellious genius born in Belleville, Illinois.

1977 had been, up to that point, the golden year of Corrado Barazzutti: a final in Monte Carlo and titles in Charlotte and Båstad. On the green clay of Forest Hills, in Queens, “Barazza” arrived at the historic semifinal without having conceded a single set to his opponents, securing for the record books what was, at the time, the best-ever result by an Italian at the American Slam.
On the other side of the net, however, stood the world No. 1, the fierce and ill-tempered Jimmy Connors, who three years earlier (1974) had claimed the Australian Open–Wimbledon–US Open treble.

The early stages of the match were marked by near-perfect balance, with the contest decided primarily by the two players’ service games; however, during the seventh game of the first set, with the score tied at 3-3, the incident occurred, which Gianni Clerici described the day after the match in the pages of Il Giorno as follows:

After leading 40-15 and having a third break point, Corrado was also the victim of a glaring error by an elderly line judge. We know that Americans have the best and most sportsmanlike line judges in the world. A backhand down the line by Connors, however, had gone out by a good three fingers. And, while the line judge remained silent, Corrado approached the ball mark and traced a semicircular mark with the tip of his racket.
While the chair umpire, old Jack Stahr, stood there awkwardly silent, and Corrado gestured in vain for the line judge to approach the ball mark, Jimmy Connors incredibly sprinted from his side of the court, caught up to Corrado—who, with his back turned, couldn’t see him—and wiped away the mark of his out ball with the sole of his shoe.
Corrado was so surprised he didn’t even have time to react. The umpire was completely dumbfounded. The 14,000 spectators in the Forest Hills horseshoe immediately began booing Jimmy Connors, who won the point but also drew a barrage of insults.

Footage of the controversial exchange at the 9:45 mark of the following video:

The episode was so sensational that for a while it was the talk of the town: journalists harassed the two athletes like wasps, bombarding them with questions and filling notebooks with endless questions. The New York crowd, a few days later, would even rally against the home team, cheering on Argentine Guillermo Vilas in the final. Clerici was no exception, and two days after the scandalous match, he unleashed his words and certainly had nothing but sweet words for the American No. 1, converting the affectionate epithet dedicated to him from “unpleasant” to “bastard.” The calm article, a true gem of Clerici’s writing, reports a conversation bordering on the surreal that took place between Clerici and Connors in the locker room after the match, witnessed by the stunned Pietrangeli and Barazzutti (the latter besieged by journalists):

“It seems to me you’ve got your feet on my pants.” “Still less serious than wiping a ball mark off with the soles of your shoes.” Jimmy Connors stood there naked, squeezed up against the metal locker with me by about thirty journalists who were swarming around Barazzutti, with their backs turned to us. […] “Get out of here so I can get dressed,” the Bastard hissed. “Are you going to tell me if you saw the mark from that ball you wiped away?” Jimmy looked around, reassured by the presence of his bodyguard and a cop who was shooing away the few people who actually had the right to be there: “I’ll tell you later. Are you going to get out of my way? Do you understand English?” “That’s not English, you thief!”
Nicola Pietrangeli looked at me in disbelief. “It seems to me we’re all going crazy,” he muttered, with all the wisdom of his 44 Roman years. “I wish Panatta were here,” I snapped, stepping back from the fray to avoid causing an international incident. “I wish Adriano had been here instead of Corrado. He would have landed a nice right hook on him, Barcelona-style, and taught him a lesson.” Nicola shook his head, and Corrado looked at me with a mixture of amusement and bewilderment.

After defeating Barazzutti, Jimmy went on to lose in the final to Vilas, winning only one set. His calm reaction to the defeat is recounted by Clerici in an article dated February 24, 1988, in La Repubblica:

Jimmy was furious. He stormed out of the club, without even changing, cursing the crowd and even New York! “I’m never coming back to this shithole town,” he shouted at the reporters who had chased him to the black limousine. It was then that I gave Jimmy a name: “The Antipatico,” which obviously only found success in Italy.

The opening of the September 12, 1977, article, which covered the Vilas-Connors final, is also amusing:

Whoever Barazzutti hurts, Vilas destroys. It might not be worth dusting off the sacred texts for a fool like Jimmy the Bastard, but I must confess that, at the end of the match, I rushed onto the field along with a hundred other intruders to shake hands with the long-haired poet.