What was behind the Cubs' middling performance in the month of June?

The sky is falling - don't you know? With a scheduled off-day to close out June, the Chicago Cubs finish the month with their worst full-month record of the year at 13-13, a perfect epitomization of treading water at an exactly .500 winning percentage.

Meanwhile, the rest of the National League Central seemed to hit its stride in June. The reigning division champion Milwaukee Brewers entered the month's final day just two games back of Chicago at 47-37 with the team that refuses to quit, the St. Louis Cardinals, just 2 1/2 back. Four of the five NL Central teams head into July above .500 (just like everyone drew it up back in spring training, right?)

So what went wrong in June?

The Cubs' offense, as a whole, took a step back this month, with the team's batting average continuing its season-long downward trend. In April, Chicago batted .267, then dropped to .258 in May. In June, they hit a new low-water mark, batting .244 as the starting rotation fought just to keep its head above water with multiple starters struggling a great deal.

The power was still there, though. The Cubs have slugged between .442 and .453 every month this year and enter July ranked third in the National League in slugging percentage. Monster years from Seiya Suzuki, Kyle Tucker and Pete Crow-Armstrong have carried the offense and helped the club overcome a rocky situation at third base from Matt Shaw and the supporting cast.

The Cubs' biggest problem? Their lackluster starting rotation

On the pitching side of things, Shota Imanaga returned - the importance of which couldn't be overstated given the major struggles of Colin Rea and Jameson Taillon. Taillon made six startsof but posted a 5.22 FIP and 5.57 ERA, allowing seven home runs. Meanwhile, the shine has completely worn off Rea, who was brilliant in the early going. The veteran swing man's struggles from May carried over into June, and the numbers speak for themselves.

Since the start of May, a stretch of 11 starts, Rea has a 5.43 ERA and 5.85 FIP - and he's definitely the odd man out when the Cubs add to the rotation ahead of the trade deadline. There's room for improvement with Cade Horton, as well, who posted a 5.47 ERA in five starts, but the club expects growing pains with a rookie pitcher.

So, in short, the team's struggles boil down to a starting rotation that, by most measures, ranked near the bottom of the league in June. This is Hoyer's top priority in the coming weeks - and you can expect to see one, potentially more, additions to that group before we turn the page to August.