On why McEnroe did not “act up” around Borg:

[…] Bjorn Borg, whom McEnroe always refers to as his “great” rival, and with whom, on court and off, he was never (or almost never) less than civil. Interestingly, Borg is said to have been a racket thrower as a young teenager. But all traces of any temper were gone by the time he began his rise to the top of the men’s tennis game in the mid-’70s, overtaking Connors and then beginning his competition with McEnroe, which would produce several years of increasingly hard-fought tennis, as they pushed each other’s games with contrasting styles, culminating in 20 or so concentrated minutes of the most galvanizing singles ever played: their fourth-set tiebreaker in the 1980 Wimbledon final. It was a year earlier, indoors in New Orleans, in only their third match against each other as pros (Borg was 22; McEnroe 20), when their relationship as opponents coalesced. They were in the third and deciding set (which McEnroe would eventually win), and it was close. As McEnroe has recounted, “I was getting all worked up and nutty.” At 5-5, Borg had had enough of McEnroe’s antics and motioned him to the net. McEnroe thought Borg was going to berate him. Instead, Borg put his arm around him and said: “It’s O.K. Just relax. It’s O.K. It’s a great match.” [Gerald Marzorati, NY Times]