TOWER GROVE — The theory behind a shift to a four-man rotation is not as screwy as some hardliners believe. The implementation might be. Asked about the plausibility of a four-man rotation in the modern game, Cardinals pitching coach Dave Duncan said earlier this week that the concept is better on paper than it is in practice.

While working on a story for this weekend’s Spring Training Preview — set to run  in  Sunday’s Post-Dispatch —  the Bird Land entry I wrote  last week  discussing how a club could shift to a four-man rotation came up with Duncan. He said he read the article and that the argument had some traction.

It just probably wouldn’t work.

“It  always sounds better than when you try to apply it,” Duncan said. “There is logic behind it. But something always happens to screw it up.”

As we all know four-man rotations used to be the norm. But the increased importance of pitch counts  and other factors have led the  five-man rotations being not just the norm but viewed as the industry standard.  The four-man rotation is dead. Yet, so many teams truly only have four starters, at most, while  many “No. 5 starters” would be better suited as middle relievers  or cameo starters.

Looking at the makeup of the Cardinals’ current pitching staff it  appeared that a four-man rotation would be reasonable: The schedule is friendly (read  some about that Sunday) and the  profiles are there. Four starters in Chris Carpenter, Kip Wells, Anthony Reyes and Adam Wainwright and three  long-form relievers in Ryan Franklin, Brad Thompson and, in his next career evolution,  Braden Looper.

This is all covered and explained — the four-man rotation and its “shadow rotation” — in the  earlier blog entry.

What wasn’t explored there and was touched on by other comments from Duncan was how a four-man rotation would  handle the innings a five-man rotation does. Last year, the Cardinals pitched 1,429 1/3 innings. A few years ago I figured it out that the average MLB team throws 1,441 innings (1,440  2/3 in the NL and 1,441 1/3 in the AL). The rained out  Bruce Sutter/San Francisco Giants game — what would have been  my little man’s first baseball game — accounts for some of the difference.

Could a four-man rotation account for those innings?

If you assume that the four-man rotation would spin through an entire season — and that was not the argument presented previously; just holding serve until Mark Mulder returns  – then we can do the math. The front two starters would each make 41 starts and the second two would make 40. The shadow rotation would  be expected to average 54 appearances  and probably would see less than 50 each.

To protect the starters, I thought you’d have to expect less innings from them. If each starter averages 4 1/3 innings per start, that would equal about 177 2/3, 177 1/3, 173 1/3 and 173 for the four starters. That would equal:

701 1/3

Each member of the shadow rotation would then need to fill, on average, the remaining 2 1/3 to get to the eighth.  That would mean the three pitchers would throw 125 2/3, 126, and 125 2/3, respectively.  That would equal:

377 1/3

All that and the two rotations would generate a total of:

1078 2/3

From the average NL team, that leaves 362 innings for the rest of the pitching staff — the bullpen — to cover. Last summer, the Cardinals had the 10th fewest innings from their bullpen (488 innings). The White Sox used their bullpen the least (407 innings) and the Royals used theirs the most (577 2/3 innings). The average bullpen threw 499 innings. It appears the four-man rotation comes in well under that limit.

Or does it?

The tripwire of the above  paragraph’s logic  is that three members of the bullpen are now  in the  shadow rotation and therefore some of their innings need to be counted in the bullpen total because those are lost innings for the  rest of the relievers.

Still looks like the needed innings will be covered.

And that’s where Duncan’s next comment comes in.

“If you go with a four-man rotation, you have to have four guys who are capable of  doing it, of being effective and staying healthy,” he said. “Today it is hard to put  four guys together like that, who can handle that kind of demand. You would have to get four guys who physically could  handle being max’d out like that.”

Duncan  said a four-man rotation would only work if the four starters are expected to handle the same expectations they would in a five-man rotation. As discussed in the previous entry, the number of short-rest starts would be minimal for Carpenter in a four-man rotation because of how the Cardinals’  schedule unfurls in April and May. But for a whole season a four-man rotation would  clearly be taxed  under five-man expectations.

Consider the innings haul again.

If the four starters averaged just five innings an appearance, all four would be counted on to throw at least 200 innings. The shadow rotation’s responsibility would shift to 108 innings each — or, realistically, less. The real heavy lifting would be on the four starters, who could climb  to 220 innings, 230 innings even 240 innings with five-man expectations. There aren’t many innings left of the needed 1,441.

I look at that and see how the bullpen — including the shadow rotation — could play a larger role  in handling those innings.  Sharing the load of 1,441 innings in agreeable portions appears possible with a four-man rotation.

It just might dilute the impact of the team’s best pitcher(s).

“If you are using a four-man rotation, you don’t want to change what the starters have to do from what you need  from them in a five-man rotation,” Duncan said. “You don’t baby  him just because he’s in a four-man rotation.”

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One of the non-roster pitchers coming to camp this spring training is righthanded pitcher Mike Smith. Not to be confused with this Mike Smith, this Mike Smith,  this Mike Smith, this Mike Smith or this Mike Smith or even this Mike Smith. He’s this Mike Smith.

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The final pre-spring training Hot Stove League  Roundtable will be held tonight on KMOX/1120 AM  from 6:30 p.m. to 8 p.m.  I’ll join Kevin Wheeler, Ron Jacober and former major leaguer Matt Whiteside,  and we’ll preview some of the things and names to watch for  in the first few weeks of Jupiter.

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Already mentioned Sunday’s paper.

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Let’s  see … what else is there to plug? Ah, yes. Tomorrow (Friday) at Baseball America’s Web site — www.baseballamerica.com — I’ll be part of a chat on the Cardinals’ minor league system and the Top 30 Prospects discussed in here and on your bookstore’s shelves. The chat will begin at 11 a.m. St. Louis time.

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