Just what is the MLB trade deadline anyway?:
The Major League Baseball (MLB) non-waiver deadline is July 31. After the All-Star break, teams will determine whether or not they are in position to contend for the post-season. Because of free agency and the lack of a salary cap in baseball, players in the final year of their contract are often put on the "trading block" by many of the non-playoff contending teams. Smaller market teams will not — or cannot afford to — pay their better veteran players high salaries, so they will attempt to trade them to a post-season contender, in exchange for some minor-league prospects or other players who might be able to help them in the future.
The MLB waiver deadline is August 31. There is much less activity between July 31 and August 31 because players must clear waivers. Players may be acquired after the August 31 deadline; however, while they can contribute to a team's push for the playoffs, they are ineligible for postseason play. The trade deadline was instituted by MLB in response to various attempts by two New York City-based ballclubs, the Giants and Yankees, to use its financial advantages to tilt its respective leagues' competitive balance in their favor from 1917 through 1922. In the Yankees' case, most of its dealings were with the Boston Red Sox. The American League (AL) established MLB's first-ever such rule in 1920 as an indirect result of the Red Sox's sale of Babe Ruth to the Yankees. It prohibited the trading and selling of ballplayers between August 1 and the conclusion of the World Series. A uniform rule serving both major leagues, which was adopted prior to the 1923 season, set the deadline at June 15. The date, chosen by MLB Commissioner Kenesaw Mountain Landis based on a suggestion from Pittsburgh Pirates owner Barney Dreyfuss, remained in effect through the 1985 season. The rule in its current form originated with the 1986 Basic Agreement which resulted from the resolution of the 1985 MLB strike.