By Bruce Levine–

MESA, Ariz. (CBS) — With expectations to be a better team and compete for a playoff spot also comes the great unknown for the Chicago Cubs. One major factor that falls under that umbrella could be team defense. Shortstop Starlin Castro and first baseman Anthony Rizzo had quality defensive seasons in 2014, with Castro cutting his errors down to 15 last season after making 22 in 2013 and Rizzo ranking among league leaders in assists and total chances and earning respect.

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The Cubs were a better defensive team in 2014 than they were in the two previous years under the Theo Epstein/Jed Hoyer-run baseball department. But two of those plus defenders are gone — Luis Valbuena and Darwin Barney. In place of the two veterans are unknowns in the present group. Second base will feature some combination of Javier Baez, Tommy LaStella and Arismendy Alcantara. Third base will also feature several candidates, including Mike Olt, Kris Bryant and Alcantara (LaStella has also played there this spring).

The Cubs appear to be have Chris Coghlan and Chris Denorfia in the left field conversation. Dexter Fowler will be the everyday center fielder, and Jorge Soler will be the regular in right. Miguel Montero and David Ross will will the catching duties, with Welington Castillo likely to be moved by Opening Day.

Cubs manager Joe Maddon has his antenna up and is trying to get a feel how this club will defend when the bell rings for the 2015 campaign.

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“Potentially really good or potentially pedestrian,” Maddon said. “My whole point is how hard are we going to work at it? I am challenging guys to win the Gold Glove, and Starlin is one of them. Dexter Fowler is another who can win a Gold Glove. It’s in their abilities. Baez at second base is already at that caliber. We have a lot of high-end potential defenders. Now we must get the work out of them.”

In 2014, MLB run production was down to 4.07 runs per team per game, the lowest average since 1981. Thus, one-run games decided by good pitching and stable defense can make a huge difference in any team’s final record this season.

“We must have them understand the importance that defense plays in this game,” Maddon said. “The offense is not going to show up every night. We must show up with our gloves every night. Yes, it’s in their abilities to be really, really good. Our guys have to believe that defense is really important. That is the sell job going on now.”

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Bruce Levine covers the Cubs and White Sox for 670 The Score and CBSChicago.com. Follow him on Twitter @MLBBruceLevine.