NOTE the additional information on the historical significance of this letter, which has been added to the description.

Exceptional letter dated July 29, 1919 from Yankees president Jacob Ruppert to Boston Red Sox president Harry Frazeew, documenting an agreement between Frazee and Yankees partner Col. Tillinghast Huston, regarding a possible transfer of a player to Philadelphia as the final piece of a deal between Philadelphia and Boston.  The player referred to is likely pitcher Scott Perry of the Athletics.  Perry was the subject of a contractual controversy between the Boston Braves and Philadelphia Athletics in 1918, after the issue was resolved, Perry won 20 games for the Athletics.  He continued to be highly sought after throughout 1919, with multiple teams attempting to acquire him via trade.  

Interestingly, this letter does have a connection with the Boston cost-cutting moves that sent pitcher Carl Mays to the Yankees, the first of several moves that culminated with Frazee selling Babe Ruth.  A disgruntled Mays had walked off the field on July 13, pledging to never pitch another game for the Red Sox.  Many teams came calling, but the Yankees made the best offer, providing Frazee with $40,000 plus two players.  Frazee, of course, wanted to replace the pitcher, and set his sights on Scott Perry.  Perry was also highly coveted by multiple teams, and clearly this letter from Ruppert is offering a choice of players as a "player to be named" to send to Philadelphia.

Also oddly, the Mays trade was called into question when it was initially nullified by AL president Ban Johnson, who was concerned that players would essentially challenge the reserve clause by refusing to play for their teams, as Mays did.  As the Athletics did with Perry in 1918, the Yankees took to the courts, and a judge issued a temporary injunction, allowing Mays to pitch.    

LOA from James Spence Authentication.