NEW YORK — Curt Flood set off the free-agent revolution 50 years ago Tuesday with a 128-word letter to baseball Commissioner Bowie Kuhn, two paragraphs that pretty much ended the career of a World Series champion regarded as among the sport’s stars but united a union behind his cause.

St. Louis had traded the All-Star center fielder to Philadelphia just after the 1969 season. Flood broke with the sport’s culture of conformity and refused to accept the Cardinals’ right to deal him, becoming a pioneer and a pariah.

After weeks of discussions with the Major League Baseball Players Association, Flood began the union’s equivalent of Lexington and Concord, challenging the reserve clause in a first shot of a labor war that would consume the sport for more than a quarter-century.

“After 12 years in the major leagues, I do not feel that I am a piece of property to be bought and sold irrespective of my wishes,” Flood wrote in his Dec. 24 missive. “I believe that any system which produces that result violates my basic rights as a citizen and is inconsistent with the laws of the United States and of the several states.

“It is my desire to play baseball in 1970 and I am capable of playing. I have received a contract offer from the Philadelphia club, but I believe I have the right to consider offers from other clubs before making any decisions. I, therefore, request that you make known to all the major league clubs my feelings in this matter and advise them of my availability for the 1970 season.”

Flood and the union lost that fight in a lawsuit that went all the way the U.S. Supreme Court, but the union’s fight went on.

“If there had not been the person who was going to step out there and take the bullets, there wouldn’t have been anything,” Flood’s widow, the actress Judy Pace, said last weekend. “So he was the man who stepped out of the foxhole to go and challenge.”

The reserve clause was struck down in 1975 by arbitrator Peter Seitz in the case of pitchers Andy Messersmith and Dave McNally, and it took eight work stoppages from 1972 through 1995 to achieve long-term labor peace.

Flood, a .293 career hitter, was long gone from the field by then. After sitting out the 1970 season, he had 40 more plate appearances in 1971 for Washington and told the Senators he was retiring via telegraph sent from John F. Kennedy Airport in New York en route to Spain. His only further employment with a major league team before his death from throat cancer in 1997 would be as an Oakland Athletics radio broadcaster for part of the 1978 season.

“All the groundwork was laid for the people who came after me. The Supreme Court decided not to give it to me, so they gave it to two white guys,” Flood once said. “I think that’s what they were waiting for.”

Baseball’s average major league salary has risen from just under $25,000 at the time of Flood’s letter to just more than $4 million this year, an escalation testament to the power of free agency. When Gerrit Cole signed his $324 million, nine-year contract with the New York Yankees last week, the pitcher paid tribute to Flood and to Marvin Miller, the transformative union head finally elected to baseball’s Hall of Fame on Dec. 9.

“Challenging the reserve clause was essential to the blossoming sport we have today,” Cole said, later adding: “I just think it’s so important that players know the other sacrifices that players made in order to keep the integrity of the game where it is, and so I hope everybody has that conversation about Curt Flood on the bus.”

The National League adopted a reserve clause binding a player to his team in December 1879. Since 1947, Paragraph 10 (a) of every Uniform Player’s Contract stated the club could renew the existing contract “for the period of one year on the same terms.” Teams claimed the renewed contract also could be renewed under that provision.

Flood was a teammate of future major league stars Frank Robinson and Vada Pinson at McClymonds High School in West Oakland, Calif. He signed with Cincinnati for $4,000, appeared in just eight games for the Reds over the 1956 and 1957 seasons and was traded to St. Louis. He played for the Cardinals’ World Series champions in 1964 and 1967, becoming a three-time All-Star and winner of seven straight Gold Gloves. His salary rose to $90,000.

On Oct. 8. 1969, St. Louis traded the 31-year-old outfielder with Tim McCarver, Joe Hoerner and Byron Browne to Philadelphia for Dick Allen, Jerry Johnson and Cookie Rojas.

Flood issued a statement saying: “If I were younger, I certainly would certainly enjoy playing for Philadelphia. But under the circumstances I have decided to retire from organized baseball, effective today, and remain in St. Louis where I can devote full time to my business interests.”

Flood conferred with his lawyer, Allan Zerman, and met with Miller and union general counsel Dick Moss the following month for four hours over lunch at the Summit Hotel in New York and discussed plans for a lawsuit against Kuhn, the AL and NL, both league presidents and the 24 clubs. The union retained former Supreme Court justice Arthur Goldberg to represent Flood.

When the union executive board met Dec. 13 at the Sheraton Hotel in San Juan, Puerto Rico, it voted 25-0 to give Flood the union’s support and pay his legal expenses, a group that included future Hall of Famers Roberto Clemente, Reggie Jackson, Brooks Robinson, Joe Torre and Jim Bunning.

Los Angeles Dodgers catcher Tom Haller asked Flood whether race was a factor in his decision.

“I think the change in black consciousness in recent years has made me more sensitive to injustice in every area of my life,” Miller quoted Flood as saying in the union leader’s 1991 book, a “Whole Different Ball Game.” “But I want you to know that what I’m doing here I’m doing as a ballplayer. ... I think it’s absolutely terrible that we have stood by and watched this situation go on for so many years and never pulled together to do anything about it.”