There are times where his curve ball looks unhittable and others where it looks like hitters know exactly where his pitches are being located. More times than not, these Jekyl and Hyde moments happen in the same game. Those low points of his often sync up with the start of the sixth inning.

It happened again in his last start on Saturday against Colorado.

“The sixth inning again, I don’t what it is, if it’s fatigue … he just lost his command in that sixth inning,” said Phillies manager Pete Mackanin.

When asked what his struggles stem from, Eickhoff, who gave up three runs in the sixth frame, didn’t really have an answer other than that when teams figure out his breaking ball, it takes a lot away from his ability to fool hitters.

“We’ve got to go to work on that and see what that problem is,” Mackanin said.

In his career, the sixth inning has been a disaster for the right-hander. He has a career ERA of 9.75 in 28 career sixth innings. That’s the highest by far among the first seven frames (he’s only reached the eighth inning one time in his career). This season, that ERA is at a whopping 12.71.

In comparison, the 26-year-old has a 1.75 ERA through the first three innings this season and a 2.16 ERA over the first four frames. It’s the fifth and sixth innings that have become disastrous for him. He has allowed just 22 earned runs from the first to fourth inning and only three runs between the seventh and eighth inning.

When it comes to those middle two innings, he has allowed 35 earned runs — 46 percent of his ERA.

Mackanin doesn’t seem like he knows what that steep drop-off is a result of, other than fatigue. If that’s the case, at least it’s something a player can improve upon. This is just Eickhoff’s second year in the big leagues. It wouldn’t be fair to expect him to be an innings eater right off the bat.

That being said, if these issues are determined to be more mechanical than physical, perhaps this trend of his won’t be going away anytime soon. From the diagnosis Eickhoff gave, it sounds like he may have bigger issues at hand. If he is unable to get pitches by hitters as soon as they figure out his curve ball, then he’s going to really need to develop another secondary pitch and his fastball this offseason.

As the Phillies start to inch towards competing on a serious level, more and more of these younger arms will be forcing their way into the rotation. If Eickhoff wants to be among the starting five, he’ll have to figure out his sixth inning nightmares.