Charles Rex Arbogast/Associated Press
Starlin Castro: B-
Shortstop Starlin Castro entered 2014 under much criticism and has even been mentioned as a trade candidate by critics. His disappointing 2013 season saw him hit just .245 with a .284 on-base percentage. Thus far, he has rebounded and improved his offense. Through 55 games, Castro is hitting .267 with seven home runs, only three short of the 10 that he totaled last season, and two-thirds of the season remaining.
However, Castro's defense still needs to improve. He has committed over 20 errors in each of his first four seasons and is on pace to continue that streak with eight errors through 54 games.
Darwin Barney: F
Quite frankly, Darwin Barney has been awful. Barney has nearly matched his four errors from last season and is hitting an atrocious .177 with only a .245 OBP. Additionally, he has only driven in 11 runs and drawn nine walks.
Barney is in grave danger of being traded, as the Cubs have young prospects such as Arismendy Alcantara knocking on the door. Alcantara is hitting .262 in Triple-A Iowa and is projected to reach the bigs this year, according to MLB.com's Prospect Watch.
Anthony Rizzo: B
First baseman Anthony Rizzo started off the season quite hot, hitting .345 in his first 15 games. Though his average has decreased to .267, his on-base percentage is an impressive team-high .396 in 54 games, largely thanks to a team-leading 38 walks.
Rizzo has already committed two errors on defense but otherwise has been solid at first base. Overall, he has greatly improved from his disappointing 2013 and has once again become a leader on this struggling Cubs offense.
Luis Valbuena: B-
Now in his third year with the Cubs, third baseman Luis Valbuena has been splitting time with young prospect Mike Olt. While the two have played in 48 and 46 games, respectively, Valbuena has been of greater value to the club as a whole.
Despite having a decent .257 batting average, Valbuena's OBP is at a solid .380 thanks to his second-best 27 walks.
Valbuena has committed three errors at third base this season but has been flawless at second base while filling in for Darwin Barney.
Valbuena has also doubled 12 times, only one behind team-leading Castro. Valbuena has been a solid third baseman while the team develops Olt and young prospect Kris Bryant, who is ranked as the No. 8 prospect in baseball, according to MLB.com.
Mike Olt: D
Though disappointing overall this season, Mike Olt remains an enigma for the Cubs' future. Olt has been known to have vision problems; however, he insists that these are a thing of the past.
On one hand, Olt is hitting a disappointing .162 with 52 strikeouts. On the other hand, Olt is a home run behind Anthony Rizzo for the team lead, clobbering nine thus far.
Olt has also committed three errors at third, but that is to be expected for a young player early in his career regardless of the position.
If not for his home runs and 24 RBI, Olt would be an utter disappointment so far this season. Though not always reliable as seen by his .162 average, Olt can be a solid offensive weapon when playing well.