It’s June 1st. The Cubs are supposed to be running away with the NL Central right now, like the Astros and Nationals are doing in their divisions. Instead, the defending champs are 25-27, in third place in the NL Central, and only a game up on the rebuilding Reds. For a team that was being hailed as a dynasty in the making, this isn’t how 2017 was supposed to go. So what’s the deal? Why did last year’s juggernaut turn into this year’s mediocrity?

Well, to start, let’s eliminate the obvious suspect. It’s not luck. The Cubs are a .481 win% team by actual record, and a .488 win% team by BaseRuns, which strips out sequencing and looks at only the underlying events a team has managed on both sides of the ball. This isn’t a case where they’ve just been un-clutch or had a few one-run games go against them. The Cubs have are a sub-.500 team because they’ve played like a sub-.500 team.

For a team that was good at almost everything last year, there is no one area that can be pointed to as “the cause” of the slow start. You don’t go this far backwards without failure on a multitude of fronts. Let’s examine the biggest ones, and identify whether they’re legitimate causes for concern going forward.

Young Hitters Not Hitting

Kyle Schwarber‘s slow start has been well documented, but Addison Russell’s 73 wRC+ isn’t much better than the 70 wRC+ Schwarber is putting up, and it doesn’t come with the obvious BABIP correction in the future, as his current .264 BABIP is only 13 points lower than his .277 mark last year. Russell’s marginally improved his strikeout rate again, but his power hasn’t carried over from last year’s second half, and he’s not an offensive force when he’s not driving the ball regularly.

Obviously, the offensive bar for Russell is lower than Schwarber, given their highly disparate defensive abilities, but while it’s pretty easy to look at Schwarber’s track record and see offensive improvement coming, Russell’s bat remains a bit more of a mystery. Still just 23, he has plenty of time to unlock his potential at the plate, but right now, he’s not hitting the ball like a slugger; his average exit velocity on balls in the air is the equal of Joey Rickard, Andrew Romine, Carlos Ruiz, and Chris Stewart.

Russell should hit better than he has early in the season, but his continuing inconsistency at the plate gives the Cubs less of a margin for error than they did a year ago. And with Albert Almora not exactly being Dexter Fowler at the plate, Willson Contreras looking more like a solid hitter than an offensive force, and some of the superhero shine coming off Schwarber with every strikeout, the Cubs suddenly have a line-up you can pitch to. This is still a better offense than they’ve shown early on, but in order to remain a run-scoring juggernaut, they were going to need guys like Schwarber and Russell to make up for the loss of Fowler and the inevitable regression coming at other spots on the field.

That hasn’t happened, and while these guys will hit better, there are enough holes in the offensive games of the team’s young hitters to suspect that the Cubs aren’t going to match last year’s 113 wRC+.

The Defense Is A Lot Worse

Even if they brought back the exact same group of players, the Cubs weren’t going to repeat last year’s +73 UZR/+82 DRS, which put the 2016 Cubs among the best-ranked defensive teams of the last 20 years. This was an area of obvious regression, even before you accounted for Schwarber’s return to the outfield or Ben Zobrist getting a year older.

And while two months of defensive data isn’t definitive in any way, the story is mostly what we’d expect. The Cubs aren’t a bad defensive team, ranking right around average by UZR and a bit better than that by DRS, but there was just no way the team was going to allow a .255 BABIP again, and sure enough, they’re up at .296 this year.

When looking at the Statcast data, the difference is just as stark. Last year, based on the quality of contact allowed (and their walks and strikeouts), the Cubs pitching staff had an expected of .297, but the team actually allowed a .281 wOBA, biggest positive differential in baseball. This year, they have an expected wOBA of .310, but an actual wOBA of .321, one of the biggest negative differentials in baseball.

Albert Almora doesn’t appear to have been the big defensive upgrade in CF he was expected to be on reputation, and the team has used Ian Happ in CF more than they’d probably have liked in an effort to get the offense going, though he’s slumped himself of late. With Schwarber in left field, the outfield especially isn’t what it was a year ago, and this is something the Cubs will just have to live with. The 2016 defense was historically awesome, but it’s not coming back. The 2017 and beyond Cubs can still be good defensively, but they’ll probably never match what the team did in the field last year.

The Pitching Has Developed A Dinger Problem

While the team isn’t preventing runs at the same rate as a year ago, the pitching problems in Chicago have been a bit overblown. The team’s strikeout rate has gone from 24.3% to 23.9%, which is basically nothing. Walks are up from 8.3% to 9.2%, which isn’t great, but the league average is up from 8.2% to 8.7%, so relative to the yearly norm, the change isn’t that dramatic. Last year, the Cubs pitching staff had an xFIP- of 91; this year, it’s at 92. Pretty much the same.

Except xFIP normalizes home run rate, and that’s an area where the Cubs have seen an early season spike. Last year, they allowed 1.01 HR/9 (#6 in MLB), and this year, they’re up at 1.26 HR/9 (#20 in MLB). The good news is that homers are a fickle beast, and this is something the Cubs can probably expect to improve going forward. They have the third highest HR/FB% in MLB, behind only the Reds and Astros. John Lackey, Kyle Hendricks, and Jake Arrieta are set to get the most significant bounces from some inevitable HR regression, and the lack of longballs should help the team’s pitching staff look a bit better.

Overall, the early season struggles are a mixture of things that the team will have to live with, a few things they’ll hope improve, and some things they should expect to start going their way a bit more regularly. There’s no reason to think the 2017 Cubs are a bad team, or that their first two months represents a true talent level for this club, and by the end of the season, they’re still very likely to be on top of the NL Central. Over the rest of the season, our forecasts expect the Cubs to win 58% of their remaining games, and make the playoffs three out of four times.

But our projections also think the Dodgers are clearly better this year, and the Cubs aren’t the runaway Best Team in Baseball anymore. If they find a quality fifth starter in the next couple of months, perhaps they can close the gap with the Dodgers — who don’t have as obvious a weakness to improve right now — but the 2017 version of the Cubs looks more like a regular really good team than a can’t-be-beat force of epic proportions.

Basically, everything went right for the Cubs last year, and this is a more normal mix of good and bad outcomes that most teams experience. There’s still plenty of upside with this Cubs roster, and it won’t be any surprise if they catch fire and finish strong over the last four months of the season. But this team also isn’t perfect, and with some guys struggling that weren’t expected to struggle, some of the holes have been exposed. Baseball is hard. Winning every year is hard. There’s a reason it doesn’t very often.