On May 30, two days before the European Tour Nordea Masters in Sweden, the agent Gorka Guillen of IMG called Pete Cowen to arrange an urgent tuneup for one of his clients, Renato Paratore of Italy, who had shot 79 and missed the cut the week before at another tournament.

“I said: ‘I might be busy. If I have time, I’ll do it,’” said Cowen, one of pro golf’s best instructors. “Of course, none of my guys showed up for a while, and Renato was there, so I tried to explain why he gets a double-cross.” That’s a shot that flies in the opposite direction from what is intended, he said, calling it “the worst shot in golf.”

Cowen spent the next few hours retooling Paratore’s swing. In the final round of the tournament, two of Cowen’s pupils, Matthew Fitzpatrick and Chris Wood, finished tied for second, one stroke behind Paratore, who claimed his first European Tour victory.

“IMG owes me a fortune,” said Cowen, 66. “That’s the third time where I help a guy on a Tuesday and he wins, and my guy finishes second.”