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Inbox: Could Cards entertain 6-man rotation?

Reporter Joe Trezza answers questions from fans
MLB.com @JoeTrezz

ST. LOUIS -- The Cardinals return to Busch Stadium to begin a seven-game homstand Tuesday against the White Sox. Until then, let's take some time to answer your burning questions.

What are the chances that the Cardinals consider a six-man rotation including top prospect Alex Reyes in August and September to keep the starting pitchers fresh?
-- Stephen S., Tulsa, Okla.

ST. LOUIS -- The Cardinals return to Busch Stadium to begin a seven-game homstand Tuesday against the White Sox. Until then, let's take some time to answer your burning questions.

What are the chances that the Cardinals consider a six-man rotation including top prospect Alex Reyes in August and September to keep the starting pitchers fresh?
-- Stephen S., Tulsa, Okla.

The chances are slim. When asked specifically about the possibility of a six-man rotation recently, president of baseball operations John Mozeliak actually said he prefers a four-man rotation, at least in theory.

The concept of a four-man rotation isn't a new one, but it is experiencing a bit of resurgence in the game today -- albeit with a modern twist, as evidenced by the Rays. Mozeliak floated it in hypothetical terms -- not as an idea the Cardinals are considering imminently -- as more of a foil to the idea of a six-man rotation.

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All of which may sound a little radical at first. But it's not difficult to see why clubs tinker with the idea. In terms of roster construction, a six-man rotation has limits on both ends. It adds talent into the rotation, but it also takes starts away from top pitchers and reduces the bullpen by a man. The extra off-days built into the schedule this year make it even less conducive.

"When you go six-man, you're probably leaving too much on the table," Mozeliak said.

The fan impulse is understandable, with Jack Flaherty and Austin Gomber throwing so well at Triple-A Memphis and Reyes earning only good reports on his way back from Tommy John surgery. But St. Louis starters own the fourth-best rotation ERA (3.31) in the Majors, and depth is a good thing to have.

The reality is no team gets through a 162-game season with just five starters. The Cards used nine last season. Twenty-three teams used at least 10. The Mariners called on 17. Flaherty has already gotten two turns. It stands to reason Gomber, Reyes, John Gant and others will in time.

But inserting one simply to elongate the rotation limits a club's roster flexibility and reduces the impact of its top arms. Let's crunch some numbers: Over the course of full season, adding a sixth starter would reduce each starter's workload by about five starts. That could mean as many as 27 starts for the theoretical sixth man, at the expense of at least five fewer for the club's ace. In St. Louis, that means a truncated season for Carlos Martinez.

Will manager Mike Matheny and coaches consider moving Matt Carpenter down in the lineup? Are they trying to get him as many at-bats as possible to get him out of his slump?
-- Alex, Chihuahua, Mexico (via Twitter)

More likely, I think, is that we'll see Carpenter sit more often against left-handed pitching. He hasn't played in two of the past three games against a southpaw starter, and Matheny could use these days to shield him and get Jedd Gyorko into the lineup. But against righties, Carpenter will probably stay near the top of the lineup despite his slow start. The reason is twofold:

1. Carpenter has underperformed his batted-ball metrics as much as any hitter in baseball.
2. Even when he's not hitting, Carpenter's batting eye doesn't slump.

Let's tackle the first one first. Yes, Carpenter's .155/.305/.274 line looks bad. But with Statcast™, we can get more insight into how his line should look based on his quality of contact. Spoiler alert: it should look better.

Carpenter is hitting the ball hard 15.3 percent of the time he swings ("hard" is defined by Statcast™ as having an exit velocity of at least 95 mph). That's above the league average of 13.2 percent. He's also lost 97 points of expected batting average and 141 points of weighted-on-base average due to luck and the infield overshift. Both rank Carpenter among the unluckiest hitters in the Majors.

Which brings us back to the second reason. Despite Carpenter's ballooning strikeout rate, his plate discipline remains elite. He still ranks eighth in walk rate, at 18.1 percent. For context, that's higher than Tommy Pham's 17 percent walk rate, and Pham owns a .453 on-base-percentage.

What is the possibility of Greg Holland being sent down for some much needed work? I know there are contract stipulations, but I am confused as to what those are.
-- Red October Rants (via Twitter)

Holland's six-plus years of big league service time allow him to refuse an option to the Minors if the Cardinals were to suggest one. That's the limit of their ability to demote him now. They can suggest or ask Holland to accept an assignment, and it is his right to accept or decline. If he rejects, the club's choices then are to keep him on the Major League roster or remove him from it.

It should be noted that there has been little indication to suggest the club and Holland are anywhere near this point. As of two days ago, there was enough confidence in his progress to provide him with a save chance after weeks of working toward one.

At this point, Holland's service-time situation isn't much different from any other veteran who didn't use all his options as a younger player, and he has now earned the right to reject one. What makes his situation confusing is that he agreed to begin the year at Class A Advanced Palm Beach after signing late. Special language was written into Holland's contract saying the assignment was agreed to.

Do we have any updates on how Carson Kelly is doing in the Minors?
-- Adam Tarr (via Twitter)

• Track Cardinals prospects' stats

St. Louis' No. 3 prospect per MLBPipeline is hitting .226/.351/.371 with two home runs and nine RBIs through 17 games with Memphis. Kelly has thrown out two of 10 attempted basestealers, while logging the bulk of innings on the receiving end of a pitching staff that ranks third in the Pacific Coast League with a 3.05 ERA.

Tweet from @carskelly: After nearly 6 years, I finally achieved one of my goals. I promised my parents the day I was drafted I would get my degree. I am blessed with all of the support in achieving this milestone and I can���t thank you all enough! pic.twitter.com/g5p8JQMjWG

Kelly also achieved an off-the-field goal recently, earning a bachelor's degree in economics from Oregon State University.

Joe Trezza is a reporter for MLB.com. Follow him on Twitter at @joetrezz.

St. Louis Cardinals, Alex Reyes