Drew Pomeranz and Shane Greene changed teams. So did Mark Melancon, Nick Anderson and Sergio Romo. Other relievers did, too, as the Braves and Nationals overhauled their bullpens and virtually every contender -- the Rays, Brewers, Dodgers, Twins -- either added someone or attempted to.

One manager recently described bullpens as volatile stocks, with the best general managers aggressively looking to upgrade or tear down and rebuild.

Bullpens have never been more important than they are right now, and that’s especially true of postseason baseball, when some managers -- the smartest ones -- play matchups almost from the beginning. Relievers accounted for 47 percent of the postseason innings for the Red Sox on their way to winning the World Series last season. In 2017, Astros manager A.J. Hinch used all but one of his starters in relief at least once.

And maybe that’s why we saw so many contenders focus on acquiring bullpen help as the July 31 Trade Deadline approached. Every team would prefer dominant starting pitchers, but find relievers easier to acquire and cheaper.

The Astros will begin the postseason favored to win their second World Series in three seasons, in part, because they have arguably baseball’s two best starting pitchers in Justin Verlander and Gerrit Cole, and a potentially dominant No. 3 in Zack Greinke.

Still, bullpens are going to decide plenty. Here’s how they stack up for 11 teams in the postseason mix:

1. Rays

Numbers: 3.25 bullpen ERA since the Trade Deadline is the best in MLB. Also first in FIP (3.59), tied for first in WHIP (1.20) and first in OPS (.651) during that time.

Bottom line: The Rays have depth and velocity, especially with the addition of Anderson from the Marlins. According to Baseball Savant, Tampa Bay has six of baseball’s top 37 pitchers -- including Emilio Pagan in first (min. 100 plate appearances) -- as ranked by xwOBA, a number that factors exit velocity, launch angle and other data to arrive at an expected on-base average.

2. Yankees

Numbers: 3.81 ERA this month, 11th best in MLB. Also first in strikeouts per nine innings (12.0), tied for 18th in OPS (.740) and tied for 13th in WHIP (1.25) during September.

Bottom line: Closer Aroldis Chapman has upped his slider usage and regained some of his old dominance with a 0.63 ERA and .122 batting average against since Aug. 1. With Chad Green, Adam Ottavino and Zack Britton lined up in front of him, the Yankees could hardly be in better shape despite a mediocre month of September.

3. Brewers

Numbers: 2.58 ERA in September, second lowest in MLB. Also second overall this month in FIP (3.31), WHIP (1.00) and strikeouts per nine innings (11.7).

Bottom line: The veteran lefty Pomeranz, acquired from the Giants, has morphed into a dominant reliever and added depth to a bullpen that was already plenty deep. Lefty starter Brent Suter, back from Tommy John surgery, has been excellent in a relief role. Josh Hader is still baseball’s most dominant closer.

4. A’s

Numbers: 3.24 ERA this month is second in AL. Also second in the AL in batting average (.199), second in WHIP (1.07), fourth in strikeouts per nine innings (10.9) and second in FIP (3.84) during September.

Bottom line: New closer Liam Hendriks is third in MLB in xwOBA (.224), and rookies A.J. Puk and Jesus Luzardo have joined veteran Yusmeiro Petit to transform a shaky bullpen into one of the best.

5. Astros

Numbers: 3.82 ERA this month is fourth lowest among 11 contenders, .226 batting average is fifth and 1.19 WHIP is sixth.

Bottom line: This one is a projection. Roberto Osuna, Ryan Pressly and Will Harris have at times this season comprised a back three as good as any, and have allowed one earned run in 19 1/3 innings this month. That’s what the Astros are hoping for after a second half in which Osuna struggled at times and Pressly underwent knee surgery. The good news is that Pressly is yet to allow a run (while fanning five) in two appearances since coming off the IL.

6. Dodgers

Numbers: .192 batting average against this month is the lowest among contenders, and 3.38 ERA is fourth lowest. Only Rays and Brewers have a lower WHIP than the Dodgers (1.02) this month.

Bottom line: The Dodgers have all the innings in front of the ninth pretty much locked down, but they’re not going to feel good about their bullpen at a time when closer Kenley Jansen has five blown saves and a 4.94 ERA since July 16. Pedro Baez, Kenta Maeda and Adam Kolarek are closer options if Jansen’s troubles continue.

7. Cardinals

Numbers: 4.58 ERA and .242 batting average this month are both 10th among 11 contenders.

Bottom line: This bullpen could be as good as any in the National League. Closer Carlos Martinez has the stuff to be a dominant closer, and they have a deep group of arms in front of him, led by Giovanny Gallegos, who has quietly been one of the best relievers in the game. The big issue for them is lack of a dominant lefty, as Andrew Miller (3.86 ERA, 5.20 FIP) is not the force he once was with Cleveland.

8. Twins

Numbers: 3.95 ERA this month ranks eighth among contenders; .238 batting average is tied for eighth; 1.22 WHIP and .724 OPS are both seventh.

Bottom line: This group is probably a bit better than those numbers suggest. Taylor Rogers has converted 13 straight save chances, and Tyler Duffey has 26 straight scoreless appearances. Romo, acquired at the Trade Deadline, Trevor May and Zack Littell give manager Rocco Baldelli a bunch of solid options.

9. Indians

Numbers: 4.37 ERA this month is ninth among contenders, .227 batting average is sixth, and 1.25 WHIP is tied for eighth.

Bottom line: Closer Brad Hand’s return from a tired arm, and Carlos Carrasco’s relief role have given manager Terry Francona two potential impact arms to go with an assortment of other reliable late-inning options.

10. Braves

Numbers: 3.36 FIP this month is third lowest in MLB; 3.74 ERA and 1.14 WHIP are both fifth among contenders.

Bottom line: No team underwent a bigger in-season bullpen overhaul than the Braves. Trade Deadline additions of Melancon, Greene and Chris Martin haven’t all worked out, but they’ve combined with Sean Newcomb, Jerry Blevins and Darren O’Day to upgrade Atlanta’s biggest problem area.

11. Nationals

Numbers: 4.99 ERA and 1.46 WHIP this month are both sixth highest in MLB, and .259 batting average is second highest.

Bottom line: The Nationals have used 24 relievers to find a combination that works. They hope they’ve found it with Sean Doolittle, Daniel Hudson, Hunter Strickland and Tanner Rainey pitching the late innings. Doolittle hasn’t looked like himself this year, and he recently spent time on the IL with right knee tendinitis. Manager Dave Martinez will likely ask for more from his starters than any other manager this October, and perhaps even use his fourth starter, Anibal Sanchez, in a relief role.