It was Oct. 9, 1987, and the Giants were leading the St. Louis Cardinals 4-0 in Game 3 of the National League Championship Series at Candlestick Park.

Jeffrey Leonard was having the postseason of his life. The Giants left fielder had homered in each of his first three games of the series, frustrating St. Louis pitchers with his bat and irritating the Cardinals with his trademark home run trot.

But in the fifth inning, Cardinals pitcher Bob Forsch decided he had seen enough.

What happened next became one of the most controversial moments of the 1987 postseason.

And nearly four decades later, some members of that Cardinals team still consider it the moment that changed the series.

Leonard, nicknamed "HacMan," had developed a distinctive home run celebration known as "one flap down." As he rounded the bases, he allowed his left arm to hang motionless at his side.

The routine delighted Giants fans but infuriated the Cardinals.

According to Graham Womack of The Sporting News, Leonard's celebrations had become a major source of tension between the clubs.

The Cardinals believed Leonard was showing up their pitchers. Leonard viewed the routine as part of his personality and competitive nature.

Things finally came to a boiling point in Game 3.

With the Giants leading 4-0, Forsch entered in relief of starter Joe Magrane. In the fifth inning on a 1-1 pitch, Forsch drilled Leonard with a fastball.

Leonard believed the pitch was intentional because of the home run celebrations.

Forsch denied throwing at Leonard intentionally.

In Womack's retrospective, Magrane recalled the reaction from the St. Louis dugout following the pitch.

"There was a lot of, 'Take that and your One Flap Down stuff' coming from our dugout," Magrane said.

The pitch didn't immediately change the scoreboard.

In fact, it gave the Giants another baserunner.

But what happened afterward proved just as important.

The Giants loaded the bases with one out, threatening to put the game beyond the Cardinals' reach.

Instead, Forsch retired Chili Davis on a pop-up and Will Clark on a fly ball, escaping without a run.

The Cardinals suddenly had life.

St. Louis scored twice in the sixth inning, with Jim Lindeman delivering a two-run home run.

Then came the seventh.

The Cardinals erupted for four runs, highlighted by a two-run single from Vince Coleman, turning a four-run deficit into a 6-4 lead.

The Giants managed another run in the ninth, but the Cardinals held on for a 6-5 victory.

The Cardinals had taken a 2-1 lead in the series and the emotional atmosphere had changed.

As Magrane told Womack, "We as a team thought that that really, really woke us up,” Magrane said. “Because the Giants had us on the run, Candlestick was going crazy and we knew we had two more games there.”

Other Cardinals players shared that interpretation but Leonard wasn't intimidated.

The following afternoon, he homered again, this time off Danny Cox in Game 4, helping the Giants even the series.

It was Leonard's fourth home run in four consecutive NLCS games, establishing a postseason record at the time.

The Giants won Game 5 as well, taking a 3-2 series lead back to St. Louis.

For a brief moment, it appeared Leonard and the Giants would have the final word.

Instead, the Cardinals delivered one last reversal.

Lefty John Tudor shut out the Giants 1-0 in Game 6 in a hard fought showdown with Giants left hander Dave Dravecky, who had pitched six strong innings while giving up one run and striking out eight.

The Cardinals overwhelmed the Giants in Game 7, with utilityman extraordinaire Jose Oquendo delivering a three-run home run in a 6-0 St. Louis victory.

Leonard, despite the controversy, was named NLCS Most Valuable Player after batting .417 with four home runs and five RBIs.

He became the last player to win the award while playing for the losing team.

When former Giants first baseman was dealt to the Cardinals from the Baltimore Orioles at the 2000 trade deadline, he ran into the retired Forsch before a Cardinals home game.

"I came up to him and said, Bob I want to thank you and I shook his hand," Clark said during an interview with Cardinals broadcasters Dan McLaughlin and Ricky Horton in 2019. "He said for what Will? I said, thank goodness you didn't drill me in the ribs."