Percy Rosberg next to a signed poster of a young Björn Borg playing at the French Open

It is from the Salk-hallen that you need to pass, where the young Borg came to take lessons from Percy Rosberg, his first coach, 83-years-old today, still here. Rosberg says: "I taught Borg how to be free not changing his two-handed backhand. Coaches from around the world were asking: tell us your secret. There was an organization. The Federation gathered talents aged 12-18 in Båstad. They were together, they played against each other. It was stupid to change. Now everyone is locked up in their little circles and that's how everything came to an end."

He indicates the empty courts. "The boys could come here and play. If the court is not booked by an adult, for them it’s free. But they don't care. They are stuck to those electronic devices that dislocate their inches or go to the gym to build their muscles.

Tennis was an excuse to see the world. Maybe today they live well with their parents. After a defeat they want to come back home, we were looking for another tournament for a rematch."

Sweden has changed in the meantime. At the time when Borg showed up, the  Social Democrat party was leading the country for the 44th year. Olof Palme had introduced the maternity allowance, salaries were growing by 30 percent, Sweden spanned the US in income per capita.

With the abolition of marks at primary school, tennis entered schools as official sporting activity. The country would convert the hockey spaces to the new mainstream sport, while in this mild May that Stockholm is enjoying, the free court of Kastellholmen is deserted. There are still 4,500 courts in the country, 900 indoor. 423 clubs, 109,000 card holders, but only 11,440 agonists.