Even though the Diamondbacks lost on Wednesday, they did still win the series against the Reds. Now, granted, many teams have won series against the Reds, but for Arizona, this was a much-needed step forward. You might remember that the Diamondbacks opened the season on a tear; they didn’t lose their first series until the middle of this month. Through play on May 1, no team in either league had a better record. Critically, nine games in the standings separated the Diamondbacks from the Dodgers. That particular gap is now down to two games, as Arizona fell on hard times. Since play on May 2, no team in either league has a worse record. After winning 21 of 29, the club has dropped 19 of 26. It’s not a lethal collapse, but all the early gains have been erased.

Here’s the Diamondbacks’ season, in visual form:

Since getting to 21-8, the Diamondbacks’ playoff odds have dropped by 50 percentage points. That’s easily the biggest drop over the span of time — the Blue Jays are down 36 points, and the Mets are down 27. There remains plenty of time to turn this around. The injury bug has been especially hungry. But it’s worth reflecting on exactly what’s happened. In certain ways, Arizona’s May has been historic.

How do you explain such a terrible month? And I’ll note here that the Diamondbacks don’t play on Thursday, so all their May numbers are in and official. When things go this poorly, it’s always about more than one or two players. It requires more of a team-wide effort. Unsurprisingly, the club’s pitching was worse in May than it was in April. And yet, that being said, in May, Arizona’s team ERA was basically league average. Not good, but also not bad. You want to see bad? You want to know how something like this can happen? Here is every team’s May wRC+:

I know that, for now, wRC+ might not be totally fair to Diamondbacks hitters, because the park factors haven’t caught up to the new playing environment. But that doesn’t really matter here, for these purposes. Since the start of the month, the Diamondbacks rank second-worst in team strikeout rate. They rank worst in team isolated power. They rank worst in team BABIP. They rank worst in team average, and on-base percentage, and slugging. They rank worst in team wOBA, which is park-unadjusted, and they’re worst in wOBA by 23 points. Over his entire major-league career, Jeff Mathis has managed a wOBA of .250. The Diamondbacks spent a month hitting almost as bad as Jeff Mathis. That’s a sure-fire way to tank your place in the standings.

Baseball Reference provides a team-based game-log feature. Using that and switching now to OPS, here’s how the Diamondbacks’ team mark has moved with every game. This is cumulative; for the first game, only the first game counts. For the second game, the first two games count, and so on from there.

It’s beyond obvious that the lineup was awful. We can move on to the truly fun stuff — the historical context. I apologize for constantly changing the stats, but I can only go on what I have available. So making use of the Baseball Reference Play Index, I decided to take a look at sOPS+. All it is is a comparison of performance in a given split to the league-average performance in the same split. Going back to 1998, here are the ten worst offensive months in Diamondbacks franchise history:

Most Dreadful Months Team Month Year Games sOPS+ ARI May 2018 27 60 ARI August 2004 26 70 ARI June 2008 27 74 ARI Sept/Oct 2004 30 78 ARI May 1998 29 80 ARI August 2012 29 81 ARI July 2004 28 81 ARI Sept/Oct 2014 26 81 ARI May 2004 29 82 ARI Sept/Oct 1998 24 82 SOURCE: Baseball-Reference sOPS+ compares team performance against the league average for the split.

The Diamondbacks had never been this bad in a calendar month. I know that using calendar months is kind of arbitrary; it would be better to compare to other 25- or 30-game stretches. But that’s simply far less searchable. So anyhow, in May, Arizona put up a team sOPS+ of 60. Here are the ten worst offensive Mays for any team on record:

Most Dreadful Mays Team Month Year Games sOPS+ ARI May 2018 27 60 SLB May 1930 27 61 HOU May 1964 31 61 CHW May 1910 23 62 CLE May 1910 23 62 PHI May 1989 26 62 WSH May 1915 20 63 CIN May 2001 28 63 STL May 1918 27 65 CHW May 1948 27 65 SOURCE: Baseball-Reference sOPS+ compares team performance against the league average for the split.

It’s close, but by this measure, the Diamondbacks take it. There is, at least, an argument that no team has ever had a worse-hitting May. For what it’s worth, there have been worse-hitting other months. If you can believe it, in April of 2003, the Tigers managed an sOPS+ of 38. In June of 2014, the Padres managed an sOPS+ of 42. The Diamondbacks haven’t hit an all-time low for any month. But, I mean, there have been a lot of Mays. There’s been a lot of baseball. It’s little consolation that the Diamondbacks aren’t coming off the worst-hitting month that anyone has ever seen. Having perhaps the worst May is sufficiently upsetting.

There’s blame for this to go around, some of it having to do with performance, and some of it having to do with misfortune. A.J. Pollock is one of the best hitters on the roster. He’s hurt, and ranked eighth on the team in May plate appearances. Steven Souza Jr. is hurt, and tied for ninth on the team in May plate appearances. Jake Lamb was hurt, and ranked 11th on the team in May plate appearances. But then, no one batted more in May than Paul Goldschmidt. That should be good, right? He struck out too much, and slugged .278. David Peralta slugged .305. Ketel Marte slugged .287. Nick Ahmed slugged .281, and Jarrod Dyson slugged .260, and Chris Owings slugged .247. The two best hitters on the team in May were Daniel Descalso and John Ryan Murphy. Murphy might be figuring something out; word is, they’re going to try to play him more often. But Daniel Descalso is Daniel Descalso. He’s never been anyone but Daniel Descalso. Imagine how much worse it would be if not for his little surge.

It should go without saying the Diamondbacks are better than this. Over three games against the Reds, they just scored 21 runs. When you have a data point extreme enough that it’s of historical significance, you should always, as a rule, expect regression toward the mean. And yet this is exactly the downside of the Diamondbacks’ construction. As good as the opening roster might’ve looked on the surface, it wasn’t a roster supported by depth. Even at the best of times, the Diamondbacks are held together by floss and scotch tape, and now that some of the best players are either injured or scuffling, there aren’t enough reinforcements. Pollock is going to return to the team. And me, I still choose to believe in Goldschmidt. But Pollock is still on the sidelines, and Goldschmidt is still striking out too much. A miserable May brought the team back to the pack. A miserable June would jeopardize the season.