It is a disappointing reality that today’s baseball heroes appear to have no sense of loyalty to their teams; they will hire an agent to find which team will pay them the most money, sign the contract, put on the new uniform and go to work.
Only the very old Red Sox fans, who now fondly recall that romantic notion of team loyalty, and the very young ones, who are still unaware that their hero will desert them–even play for their arch rival Yankees–for a few extra dollars.
Some recall the “Old Days” and wonder why MLB players no longer play for the same team for their entire career. They remember “Teddy Ballgame” and “Yaz,” and Jim Rice, and recently, an Old School modern era player, “Tek,” who played their entire professional career in the Boston uniform.
Now, although fans want to believe that Ellsbury would take less money, just to stay with his team and the city that supported him when he was a rookie, they are quickly reminded that the motto for today’s generation of MLB players is “Show me the money!”
"What happened to those Good Old Days?"
Q: When did the players become so greedy?
A: December 23, 1975.
Prior to that day, players were chained to their “home team” by the “Reserve Clause,” which bound a player to his team for as long as the team, not the player, desired. 
Even after the contract itself expired, a player remained tied to the team. He could be traded, sold, or released, but the player himself could not initiate any moves on his own.
As was pointed out in a comment by Mr. Curt Flood, Jr., the rise in salaries did not suddenly shift:
“…the pendulum began to inch in the other direction, however, a million dollars a year was still considered a blue-chip player salary level as late as 1990. What’s more, I have it on fairly good word that Jean Yawkey was paying the 1986 Red Sox ball club from revenue that was generated by the organization in the 60’s. So players had at least two decades of catching up to do, in order to close the disproportionate, inequitable, and illogical imbalance chasm caused by MLB and club owner-cherished “Reserve Clause.” “
The reserve clause had its origin at the end of the 1879 National League season and soon evolved into the form it would keep well into the second half of the 20th century.
The first effort to eliminate the Reserve Clause came in 1969, when, with the backing of his fellow players:
“Curt Flood filed a lawsuit against baseball, which challenged the sport’s exemption from antitrust laws and in turn the reserve clause. Flood, an outfielder who decided to fight baseball after being traded from the St. Louis Cardinals to the Philadelphia Phillies in October of 1969, ultimately lost his case; however, the battle produced additional solidarity among the players.” 
A few other court challenges were also denied. 
Then, suddenly, the MLB owners were horrified to find out that two pitchers, Andy Messersmith of the Dodgers and Dave McNally of the Montreal Expos won their court case against the Reserve Clause.
At the heart of the Players Association’s case before the arbitration panel was the argument that the word “one,” when used in Paragraph 10A, meant a single year rather than a rolling number of one-year renewals stretching into perpetuity.
The owners’ argument, actually given by the Los Angeles Dodgers, the team trying to retain Messersmith, was that they had the right to renew the entirety of the contract, including the right to renew the renewal provision.” 
On December 23, 1975, Santa arrived early for the MLB players; Peter Seitz, the impartial arbitrator, ruled for the players. On the final page of the decision, Seitz declared that Messersmith and McNally were free agents. 
Players were no longer bound to their teams, as free agents they could negotiate a new contract with any team in MLB. The Law of Supply and Demand kicked in and salaries skyrocketed.
Prior this ruling in 1975, players like Willie Mays and Mickey Mantle were making headlines when they signed for over $100,000; Mays’ top career salary was $160,000 in 1973 and Mantle’s was $100,000 in 1968.
Would the players from the Good Old Days have remained with their teams for their entire careers, if they were free from the Reserve Clause?
A frequently recalled quote captures the essence of the romantic notion that players in the Old Days were not there for the money, but for the sheer joy of playing the game:
“We would have played for nothing.”
It implies that in those Old Days players were not driven by greed, but that’s not the whole story.
Reflecting on how Negro League Players were shunned by professional baseball, Negro League outfielder, Willie Grace, lamented:
"“Heck, we would have played for nothing.”"
While the Reserve Clause was emancipation from servitude for the players, it created a new system, where players became mercenaries, who would play for the highest bidder and loyalty to a team and its fans became a naive, romantic illusion.
There must be a way to develop a system that assures that the players receive proper compensation for their performance and not outrageous amounts of money that are wildly disproportionate to the salaries of their fans.
 Contract language:
The clause was codified into the Uniform Player’s Contract, eventually becoming Paragraph 10A of the document:
On or before December 20 (or if a Sunday, then the next preceding business day) in the year of the last playing season covered by the contract, the Club may tender to the Player a contract for the term of that year by mailing the same to the Player at his address following his signature hereto, or if none be given, then at his last address of record with the Club. If prior to the March 1 next succeeding said December 20, the Player and the Club have not agreed upon the terms of such contract, then on or before 10 days after said March 1, the Club shall have the right by written notice to the Player as said address to renew this contract for the period of one year on the same terms, except that the amount payable to the Player shall be such as the Club shall fix in said notice; provided, however, that said amount, if fixed by a Major League Club, shall be an amount payable at a rate not less than 80 percent of the rate stipulated for the next preceding year and at a rate not less than 70 percent of the rate stipulated for the year immediately prior to the next preceding game. [James B. Dworkin, Owners versus Players: Baseball and Collective Bargaining, Boston: Auburn House Publishing Company, 1981, p. 63.]
 “Messersmith Ruled Free Agent,” Minneapolis Tribune, Wednesday, December 24, 1975, p. 1C (Associated Press story); “Messersmith Free” by Red Foley, New York Daily News, December 24, 1975, p. 48; “Messersmith Decision Stuns Baseball Owners,” Atlanta Constitution, December 24, 1975, p. 13 (Associated Press story); “Arbitrator Frees Messersmith, Then Is Fired, St. Louis Post-Dispatch, December 24, 1975, p. 1C (Compiled from News Services); “Panel Frees Messersmith, McNally,” Chicago Tribune, December 24, 1975, p. 1, Section 2 (Associated Press story); “Two Pitchers Declared Free Agents, Baseball’s Blockbuster,” San Francisco Chronicle, December 24, 1975, p. 35; “Ruling Gives Baseball Players Free-agent Status,” St. Paul Pioneer Press, December 24, 1975, p. 12 (Associated Press story); “Reserve Clause Dealt a Blow,” Washington Post, December 24, 1975, p. 1; “Arbitrator Rules 2 Pitchers ’Free’, Washington Post, December 24, 1975, p. C1 (Associated Press story); “Arbitrator Frees 2 Baseball Stars” by Joseph Durso, New York Times, December 24, 1975, p. 1.
 (Other unsuccessful court challenges to the reserve clause as well as baseball’s exemption from federal antitrust laws, which was established by the U. S. Supreme Court in 1922, had been filed by Danny Gardella and George Toolson. Gardella had been blacklisted by major league baseball after having played in the outlaw Mexican League; his case was eventually settled out of court in 1949. Toolson was a New York Yankees farmhand who sought his freedom as a means of having a better chance to reach the majors with another organization. Toolson lost his case as the Supreme Court reaffirmed baseball’s antitrust exemption.)[http://milkeespress.com/reserveclause.html]
 Interview with Marvin Miller, May 22, 2003; Miller, A Whole Different Ball Game, p. 250.