One of baseball's best characteristics is how you can't hand the ball to your running back 40 times a game or feed Shaq till he bursts. No matter how good A-Rod may be, he'll never bat more than once every nine times. Randy Johnson can pitch just once every four or five days, period. (And Derek Bell plays, well, whenever he kinda feels like it.)

Nowhere is this dynamic more apparent than the struggle most teams face trying to fill the back end of their rotations -- the No. 4 spot, which will make the same 33-35 starts as the three ahead of it, and No. 5, which depending on how days off fall still takes the mound about 25 times. That's 60 starts, more than a third of your games, being made by guys who might be major leaguers in paycheck only.

	No. 4 starter Cory Lidle was 13-6 with a 3.59 ERA for the A's last season.

Teams which strike gold that deep, like the Mariners did last year with Paul Abbott and the A's with Cory Lidle, get a huge leg up on the competition.

"They're huge," A's ace Tim Hudson says of Lidle and Oakland's No. 5, Eric Hiljus, a revelation who went 5-0 with a 3.95 ERA in that role. "Everyone talks about our top three, me and Mulder and Zito, but Cory was our best pitcher at times last year and a lot of people don't realize that. A lot of 4 or 5 guys you chalk up as a tough game to win. We're expecting to win with those guys, and a lot of teams can't say that."

Even some contenders. The World Series-champion Diamondbacks, of course, don't have much past Randy Johnson and Curt Schilling, and are going on the back end that makes Calista Flockhart's look fat: Rick Helling (12-11, 5.17 with the Rangers last year) and Brian Anderson (3-9, 5.46 as a starter with Arizona). The Braves have the enigmatic Kevin Millwood and the vegematic Albie Lopez.

Much of a 4 or 5's success has to do with outside factors. A strong bullpen is critical because back-end starters usually don't last as long as front-end guys. And Abbott went 17-4 last year not just because of the Mariners' strong bullpen but also in large part to getting 7.79 runs per nine innings of run support, by far the most in baseball. (He has been bumped up to No. 3 with Aaron Sele's relocation to Anaheim.) "I don't think he'll win as much as he did," one scout said. "He'll have the same stuff without the same cushion."

Of course 4s and 5s don't often face off against their counterparts on other teams because rotations get jumbled after only a few weeks. (Imagine Robert Ellis' horror when for his third Diamondbacks start last year on April 26 he matched up with one Greg Maddux.) Therefore labels can be only psychological. "I never considered myself an ace (in Texas)," Arizona's Helling said. "It just worked out that way. Coming here, I'm not. I'm not gonna be that guy who's looked at to stop a losing streak. I don't have that distinction here."

Finding two guys who can pitch even .500 ball versus a pair of stiffs who blow out your bullpen several times before you axe them can make several games' difference in the standings come September. So even the A's, Yankees and Twins, whose front-three locomotives are their biggest reasons for contending, must give plenty of thought these next 10 days to the rotation's rear cars. Teams wind up with different pairings -- which are fluid and hard to predict before final roster cuts -- but they usually break down into one of several categories, among them:

	Ainsworth

	Rueter