The trade deadline wasn't always a thing. There had been deals here and there, although for a long period of time the trade deadline was set at June 15. The sport didn't want the integrity of pennant races affected by rich teams buying veteran players from cellar dwellers to help out down the stretch.
The July 31 non-waiver date wasn't established until 1986. One of the first big trades that people remember was the Detroit Tigers trading a Double-A pitcher named John Smoltz in 1987 to the Atlanta Braves for Doyle Alexander, who went 9-0 with a 1.53 ERA and helped the Tigers win the American League East. But that trade actually happened in August.
If there were two trades that changed the way front offices operate, it was the New York Mets trading David Cone to the Toronto Blue Jays in 1992 for Jeff Kent and Ryan Thompson. Cone was an impending free agent and helped the Blue Jays win the World Series. Except that trade happened in August as well, meaning Cone cleared waivers. Three years later, after he had signed with the Royals and later was traded back to the Blue Jays, Cone -- once again heading to free agency -- was traded on July 28 to the Yankees, helping them reach the postseason.
Those two trades set in motion the idea of the hired gun, and it soon became expected that a team fighting for the playoffs would bolster its roster at the July 31 trade deadline. Not all trade deadlines are created equal, however, and last year's was unprecedented not just in the star-level talent that changed hands, but the impact they ultimately had on pennant races in the postseason. Consider:
Yoenis Cespedes, Mets: Hit 17 home runs and drove in 44 runs in 57 games as the Mets surged past the Nationals to win the NL East.
Johnny Cueto, Royals: He didn't pitch well for the Royals down the stretch, but had two huge games in the postseason: two runs in the eight innings of Game 5 of the Division Series and then a complete game in Game 2 of the World Series.
Ben Zobrist, Royals: Filled a big void at the top of the lineup, then produced an .880 OPS in the postseason.
Cole Hamels, Rangers: He wasn't just a rental since he was signed beyond 2015, but he went 7-1 in 12 starts as Texas rallied from seven games back on July 31 to win the AL West.
Troy Tulowitzki and David Price, Blue Jays: They acquired Tulo on July 28 and then won 14 of their next 15 -- with the help of Price, who was acquired on July 30 -- as they rallied from eight games back to win the AL East.
You also had former All-Stars Carlos Gomez, Scott Kazmir and Jonathan Papelbon traded, although they failed to make the same impact. Sometimes a big name makes an impact, but the team still misses the playoffs, like Carlos Beltran going to the Giants in 2011 or Zack Greinke to the Angels in 2012. Some years there just aren't big names to move. In 2013, for example, the "big" names traded on July 31 were Bud Norris, Ian Kennedy and Justin Maxwell. The biggest name leading up to the deadline was Jake Peavy, who had a 4.28 ERA when he was traded. (Although in early July, the Orioles traded a disappointing right-hander named Jake Arrieta to the Cubs.)
So while everyone spends most of July devouring the rumors and reading up on prospects, we don't always get a landslide of All-Stars traded. This may end up being one of those years. It's possible that the two best players already have been dealt -- Aroldis Chapman to the Cubs and 2016 All-Star Drew Pomeranz to the Red Sox. If the Brewers trade Jonathan Lucroy and/or Ryan Braun, those are certainly two players who could impact playoff races, although maybe not to the extent of Cespedes and Price a year ago. Beltran and Matt Kemp would be interesting names, though maybe not all-around impact players because of their defensive liabilities.
There are some other names that have been floated out there that could spice up this deadline:
Chris Sale: This would be the big kahuna, and the Red Sox and Rangers seem to have the young players to make enticing offers, but these deals are obviously difficult to match up, and the White Sox are going to be reluctant to commit to a rebuild. However, the past two years we've seen some top pitchers traded who had extra years of team control still remaining: Jeff Samardzija to the A's and Price to the Tigers in 2014, and Hamels last year. Sale has team options through 2019.
Chris Archer: He obviously hasn't pitched as well as last year, but he brings ace-level potential. He would be expensive, with a team-friendly contract that runs through 2021.
Sonny Gray: Like Archer, in the midst of a disappointing season.
Carlos Gonzalez: These trade rumors seem to be coming more from the Gonzalez camp than from the Rockies, and the Rockies think they have a chance to be good in 2017, the final year of Gonzalez's contract.
Mike Trout: Now this would be a blockbuster ...