The MLB trade deadline is less than a week away, but teams have already seen one of the best available bats, J.D. Martinez, moved for scraps, while relief pitchers have fetched a kings’ ransom in prospects and value.

The reason for the sudden shift from value in rental bats to quality relievers in the baseball trade economy shouldn’t be too surprising: Front offices have realized that great relief pitching is a big key to winning in the postseason.

Winning in the postseason is generally a bit of a crapshoot: the very best team in the regular season rarely makes it all the way through to the postseason. The 2001 Mariners — widely considered to be one of the best teams of all time — were knocked out in the first round of the playoffs. The Cubs, the consensus best team in baseball, still had only a 26 percent chance of winning the World Series at the end of the regular season, per 538’s playoff predictions. The AL Champion Indians had a 9 percent chance.

Having a top-tier bullpen is the one similarity the Cubs and Indians shared in the 2016 playoffs: top-tier bullpens that had been bolstered by acquiring expensive relief pitchers at the deadline.

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The Cubs picked up Aroldis Chapman and the Indians traded for Andrew Miller, both from the Yankees. Both teams were also unafraid to turn to relievers to eat up innings, as 38 percent of all innings pitched by Cubs in the postseason were by relievers, and 47 percent for the Indians.

By Fielding Independent Pitching (FIP), the Cubs and Indians had the two best bullpens in the 2016 second half of any playoff team that made it past the wild card, which culminated in a World Series meeting. What set the Cubs and Indians apart from other teams with top-tier bullpens that made early playoff exits is the way the 'pens were used.

Cleveland and Chicago were unafraid to pitch their best relievers frequently and for long outings. The Cubs' Chapman registered 15 2/3 innings pitched during the playoffs, while Miller threw 19 1/3 innings for the Indians. Miller pitched more than one inning in every appearance in the 2016 postseason, and Chapman made the longest appearance of his career in Game 5 of the World Series, retiring eight batters.

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It also mattered when they were used: managers Joe Maddon and Terry Francona brought in their best relievers to face the heart of teams’ lineups in tight situations. Using their best relievers for multiple outs in clutch spots meant that the Cubs and Indians wanted to prevent games from spiraling out of hand. While this resource-intensive style of management might not work in the regular season, it’s extremely effective during the do-or-die postseason.

You can contrast this with the way Orioles manager Buck Showalter infamously kept Zach Britton sitting on the bench while Ubaldo Jiménez gave up the game winning home run to Edwin Encarnación in the AL wild-card game. Instead of bringing in his best reliever to a tight situation, Showalter held onto Britton for a save situation which never came. Baltimore had a fantastic bullpen, but Showalter operated on a regular-season mentality — not "postseason rules" — which led to an early Orioles exit.

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After seeing how both the Cubs and Indians relied successfully on their bullpens to make it through the postseason, other teams have begun to copy the strategy in hopes of pulling through the postseason. The Yankees pushed hard for David Robertson and the underrated Tommy Kahnle — who is quietly having a terrific season and striking out a career-high 16.2 per nine innings — to be included in the Todd Frazier deal. We’ve also seen reports linking the Dodgers to Zach Britton, one of the best relievers in the game. The Nationals are seemingly locked for a playoff spot, but picked up Ryan Madson and Sean Doolittle from the Athletics to shore up a terrible bullpen.

None of these teams are loading up on relievers because they think that they need to improve their 'pen to reach the playoffs. The Nationals and Dodgers are all but assured October spots with 99 percent and 100 percent odds of making the playoffs respectively (via Fangraphs). The Dodgers and Yankees are the No. 1 and No. 2 bullpens in the majors by fWAR. By acquiring as many great relievers as possible, contenders are putting together a staff of firemen to extinguish rallies in postseason games.

For the chronically underpaid, under-appreciated relief pitcher, it’s been a long time coming that teams finally realize their importance. Teams looking to be contenders focusing less on positional needs by acquiring rental bats, but instead loading up on bullpen arms, anticipating the playoffs, could be the future of the trade deadline.