The high-water mark of the Colorado Rockies’ season was June 20, when they were 47-26 and led the NL West by a half game. The Rockies had the best record in the National League and were 1.5 games behind Houston for the best record in all of baseball, and things were looking great.

The Rockies have made the playoffs just three times in their 25-year history, but every time Rocktober rolls around, it’s fun—from the mulleted Larry Walker–led Blake Street Bombers of 1995 to the legendary 21-1 streak in 2007 that convinced a nation that black sleeveless jerseys possessed magical powers to a frigid, nerve-destroying four-game NLDS loss to the Phillies in 2009. Coors Field in October is like no other setting for baseball—it’s cold, sure, but not the sickly, damp, just-walked-through-a-puddle cold of the Northeast. Not only does playoff baseball in New York or Boston make you wish you had dry socks, it’s also familiar. Even after 25 years there’s still something alien about baseball in Colorado, so going there in October feels special. The sheer size of the ballpark, with the mountains in the background, lends grandiosity to playoff baseball—like Alexander Nevsky and the Battle of the Ice.It’s purple mountain majesty, in so many words.

On June 20, the Rockies had a 94.3 percent chance of making the playoffs—just be cool, guys, and we’ll be sewing purple “Postseason” patches on the jerseys in no time. The Rockies then fell out of first place June 21 and haven’t been back since—which is fine, because around that time the Dodgers were in the early stages of a two-month hot streak that earned them comparisons to the 1998 Yankees. But the Rockies are 35-44 since June 21, and, as of Thursday morning, clinging to a single-game lead over Milwaukee for the second wild-card position. Colorado’s playoff odds have dropped to 61.8 percent, down 24.5 percentage points in the past seven days alone.

Guys, this is not what “being cool” looks like.

Colorado’s slow slide back to the pack over the past three months isn’t as severe as the Dodgers’ sudden self-immolation, and indeed, many important things have gone right for Colorado. Offensive catalyst and anthropomorphic renegade sheep Charlie Blackmon was hitting .327/.376/.605 on June 20, and since then he’s hitting .335/.417/.607. Star third baseman Nolan Arenado was hitting .302/.354/.579 at the June 20 high-water mark, .307/.380/.579 since. All-Star second baseman DJ LeMahieu was hitting .299/.361/.381 on June 20, .331/.399/.459 since.

But almost every team has a few really good players—LeMahieu, Blackmon, and Arenado have all been with the Rockies since at least 2013, and in that time Colorado hadn’t managed to win more than 75 games in a season until this year. It takes more than just a couple guys to make the playoffs.

While their stars are still producing, the Rockies have fallen off in a few predictable areas: 34-year-old Mark Reynolds was never going to hit like 25-year-old Reynolds for the entire season. He was at .297/.379/.541 on June 20 and he’s hit just .234/.322/.435 since, and that José Reyes–lookin’ batting line just won’t cut it for a first baseman in Colorado. But the Rockies have made up for Reynolds’s decline in other areas, specifically by covering their gaping hole behind the plate by acquiring Jonathan Lucroy on July 30. After a horrible first half with Texas, Lucroy has hit .286/.392/.387 since the trade. The Rockies hit .275/.334/.447 through June 20, and they’ve hit .268/.338/.437 since—the offense isn’t the problem.

Rookie left-hander Kyle Freeland, the no. 8 pick in the 2014 draft, had great success early in the season despite not striking out very many batters—pitching at Coors with a low strikeout rate is baseball’s equivalent to BASE jumping or bear-baiting. After posting a 3.42 ERA through June 20, Freeland’s since lost his spot in the rotation, though his 4.63 ERA since June 20 isn’t that bad. Freeland’s fellow low-strikeout rookie, Antonio Senzatela, has also been in and out of the rotation after an awesome first two months of the season.

It’s not all bad news for the pitching staff. For example, the Rockies’ best starter, 2013 first-rounder Jon Gray, made only three starts before June 20 thanks to a broken foot, and they were positively Hobbesian: Nasty, brutish, and short. Gray returned in late June and has since posted a 3.66 ERA with 90 strikeouts in 86 innings. They also acquired veteran reliever Pat Neshek from the Phillies on July 26. But Gray and Neshek have only done so much: Since June 20, Rockies pitchers are allowing 1.2 more hits per game and 0.9 more runs per game than they were before, despite their per-inning strikeout, walk, and home run rates holding relatively constant. The Rockies’ team ERA- went from 89 before the All-Star break to 94 afterward. That still isn’t bad, but it’s the difference between third and seventh in the National League.

It’s tough to find a big, macro-level cause for the Rockies’ surprising slide back to the pack because the last three months looked worse than they were. From Opening Day to June 20, the Rockies outplayed their run differential by a little more than three games. Since June 20, they’ve underperformed their run differential by about two and a half games. They’re neither as good as their record in the first three months nor as bad as their record since.

The easiest way to explain a swing like that is the bullpen, because the people pitching the highest-leverage innings are going to be able to do the most damage. When I wrote about the Rockies at the end of April, they were 14-9 and 7-0 in one-run games. Closer Greg Holland had a 1.80 ERA and a perfect nine-for-nine record in save opportunities, six of which came in those one-run games. Holland helped the Rockies bullpen lead MLB in win probability added in April and it wasn’t close—Colorado outpaced the second-place White Sox by 2.16 that month, or the difference between the White Sox and 17th-place Arizona. In the combined five months since, the bullpen still hasn’t matched its WPA number from April, while the run prevention numbers have hovered around “slightly better than league average.”

Rockies Pitching by Month Month ERA Rank K-BB% Rank WPA Rank Team Record Month ERA Rank K-BB% Rank WPA Rank Team Record April 10th 9th 1st 16-10 May 6th 10th 8th 17-12 June 15th 15th 15th 15-12 July 16th 30th 19th 12-12 August 9th 14th 9th 12-15 September 11th 11th 5th 10-9

But a few key relievers have fallen off in the past three months. Not counting Neshek, here are the four Rockies relievers with the highest gmLI (average leverage index when entering the game), along with their WPA and ERA on June 20.

Key Rockies Relievers Through June 20 Pitcher ERA WPA Pitcher ERA WPA Greg Holland 1.63 2.528 Jake McGee 2.45 0.658 Chris Rusin 2.82 1.183 Adam Ottavino 3.08 0.707

And here are those same four pitchers’ numbers after June 20.

Key Rockies Relievers After June 20 Pitcher ERA WPA Pitcher ERA WPA Greg Holland 5.67 -1.203 Jake McGee 5.33 0.362 Chris Rusin 2.23 1.249 Adam Ottavino 7.77 -0.664

Just narrowing it down to Holland and Ottavino puts the problem into focus: Over the first 73 games of the season, those two pitchers were worth about 3.2 wins in WPA. Over the past 79 games, those two have been worth minus-1.9 wins. A five-win swing in WPA from two relievers doesn’t get the Rockies back to “best team in the NL” but it probably gets them back to “be cool.”

Pretty much every year, at least one team with a good bullpen jumps out to a hot start thanks to a good record in one-run games. Sometimes, as with last year’s Rangers and three different Orioles teams in the past decade, that luck continues all year. Other times, as with the 2003 Royals and 2010 Padres, that team slowly regresses over time and eventually slides back toward the pack, like a cyclist on a breakaway trying to outlast the peloton. That’s what’s happening to the Rockies now—they were never a true-talent .644 team, but they were supposed to still be good enough to stay out ahead of the charging NL wild card pack after being given that big of a head start. The cushion has run out and the fate of Rocktober rests on a 10-game sprint to the finish line.