Thirteen players who ranked as their organization's top prospect in the offseason have suited up for the big league club this season, but not all the rookies have been ready for prime time.

The Blue Jays' Kyle Drabek ran up a 5.70 ERA through 14 starts to earn a demotion to Triple-A. Reds fireballer Aroldis Chapman walked 20 batters in his first 13 innings and suffered a similar fate, though he's back in Cincinnati now. First baseman Brandon Belt went 12-for-57 (.211) and had spent as much time in Triple-A Fresno and on the disabled list as in the Giants lineup. Chris Sale ran up a 5.91 ERA and 1.59 WHIP in 10 April appearances for the White Sox before settling in.

These are not their stories. Instead we'll focus on those rookies who stand above their contemporaries for their play through the season's first three months. Statistics here capture a snapshot of each player's performance at the end of the day June 30, roughly the season's halfway point.

Rookies are organized into four groups so that performances can be compared more directly. Players are divided into starting pitchers, relief pitchers, up-the-middle defenders and corner players, because no one ought to expect a middle infielder's raw offensive production to look like a corner outfielder's.

For rookie rundowns going back five years, check out the 2007, 2008, 2009 or 2010 midseason lists.

An asterisk (*) denotes a lefthanded batter or thrower and a pound sign (#) signifies a switch-hitter.

UP-THE-MIDDLE ROOKIES
Catcher, Second Base, Shortstop & Center Field

Catcher J.P. Arencibia (Blue Jays, age 25) typifies Toronto's offensive attack with his homer-happy, low on-base approach. (The Blue Jays rank third in the American League in home runs, but just eighth, and below the league average, in on-base percentage. It adds up to a fifth-place showing in runs scored.) Only AL all-star starter Alex Avila (.235) sports a higher isolated power than Arencibia (.232) among catchers this season, and with 12 home runs already, Arencibia has Geovany Soto's total of 23 homers for the ’08 Cubs in his sights. That's the high water mark for rookie catchers in the past decade. But in order to take that next step, Arencibia will need to avoid getting himself out so frequently. But that's been the story for some time for a man who owns a career .319 on-base percentage in the minors.

Keep an eye on: The Nationals' Wilson Ramos has more defensive polish behind the plate than Arencibia, but his first-half batting line (.238/.317/.389) had been propped up by a walk rate (9.1 percent of appearances) he had never shown in the minors. His power and catch-and-throw skills are real, however.

Second baseman Danny Espinosa (Nationals, age 24) breezed through the minors in two seasons and has turned in the finest offensive season by a rookie to this point. The erstwhile shortstop also has made positive defensive contributions, making him an early contender for Rookie of the Year. Espinosa leads all rookies in home runs (15), RBIs (48) and slugging (.465)—but also with 72 strikeouts, which explains the .238 average. The switch-hitter has struck out less frequently (22.5 percent of at-bats) and hit for more power (.238 isolated power) as a righthanded batter than as a lefty (26.2 percent, .218 ISO), which has dragged down his overall line. Espinosa's minor league track record suggests that he will hit for power in roughly equal measures from both sides of the plate, but that he will continue to swing and miss more often from the left side. As a lefty batter in 2009-10: 28 percent strikeout rate, .200 ISO. As a righty: 21 percent, .187 ISO.

Keep an eye on: Jemile Weeks has been a revelation for the Athletics in batting .309/.349/.469 with 10 extra-base hits and six steals through his first 81 at-bats. His ascendance encouraged Oakland to trade second baseman Mark Ellis to the Rockies.

A number of rookie shortstops have logged playing time this season while filling in for injured incumbents. Among them are the Dodgers' Dee Gordon (Rafael Furcal) and the Yankees' Eduardo Nunez (Derek Jeter). Meanwhile, the Giants' Brandon Crawford and the Twins' Trevor Plouffe (if only briefly) supplanted underachieving regular shortstops Miguel Tejada and Alexi Casilla. But the only rookie shortstop to serve in a regular role from Opening Day, while contributing on both sides of the ball, has been Elliot Johnson (Rays, age 27), a man who spent nine years in the minors and did not play more than 20 games at short until last season. In fact, he wasn't even necessarily a part of the Rays' future last April when they removed him from the 40-man roster. But Johnson batted .319/.375/.475 in 481 at-bats for Triple-A Durham, while playing both middle-infield and both corner-outfield posts, to earn his way back into Tampa Bay's good graces. This season he's served in a rough platoon with lefty-batting shortstop Reid Brignac, he of the .450 OPS. The switch-hitting Johnson has batted .250/.388/.300 in 40 at-bats versus lefthanders, while providing value on defense and on the bases. A utilityman is born.

Recent rookie center field classes have given us Jacoby Ellsbury, Brett Gardner, Austin Jackson, Andrew McCutchen and Colby Rasmus. This year's group pales in comparison. Lefty-hitting Ben Revere (Twins, age 23) has continued to do the things that got him to the big leagues in the first place—slash singles to all field, steal bases and run down the ball in center field.

ON-THE-CORNER ROOKIES
First Base, Third Base, Left Field, Right Field & Designated Hitter

Mark Trumbo (Angels, age 25) stepped into the first-base void created when Kendrys Morales did not answer the bell this season because he required a second surgery for his broken ankle. Trumbo tied for the minor league lead with 36 home runs last season with Triple-A Salt Lake, and then added five more in 28 games in the Venezuelan League. He has mashed 13 homers through the first half of this season, albeit with the same low on-base tendencies (career .330 OBP) he showed in the minors. Trumbo's makes consistent contact and is strong enough to hit mistakes a long way, but he has enough holes in his swing that me may never hit for a high average.

Freddie Freeman (Braves, age 21) hit just .225 in April, but he collected three hits in a May 4 doubleheader and proceeded to go on a tear, batting .301/.348/.462 with 18 extra-base hits in his next 49 games. (He started slowly with Triple-A Gwinnett in 2010 as well, posting a .757 OPS in April and May, before finishing out the year at .973.) A more well-rounded player than Trumbo, Freeman is penciled in as a DH on this rookie team, but he probably will supplant the Angels first baseman by season's end.

Keep an eye on: First base has been a stacked position for rookies this year. The Royals' Eric Hosmer had cooled to a .268/.316/.404 line through 198 at-bats after hitting .333 and launching two homers in his first six games. A pair of National League West rivals unveiled rookie first basemen this season, but it may be 2012 before the Giants' Brandon Belt (.609 OPS through 57 at-bats) and the Padres' Anthony Rizzo (.697 OPS through 57 at-bats) can be counted on as middle-of-the-order run-producers. Both have shown discerning batting eyes with strong walk rates, giving them something to build on once the hits begin falling.

New York claimed Justin Turner (Mets, age 26) on waivers early in the 2010 season, but they could not have known how valuable he'd become one year later. After the Mets jettisoned Rule 5 pick Brad Emaus (.162 with zero extra-base hits) in late April, Turner got the call from Triple-A Buffalo and provided instant value by hitting for average and playing solid defense at the keystone. Turner shifted to third base when David Wright went down in mid-May and continued to serve as a traditional two-hole hitter with his ability to make contact and handle the bat.

Keep an eye on: Turner does not bring the power to be a prototype third baseman, and that's where the Royals' Mike Moustakas comes in. He had only one extra-base hit (a home run) through 16 games as part of a .263/.354/.316 batting line, but AL pitchers won't be able to keep him in the park for long.

The ranks of minor league corner outfielders who can mash are thin, and that shortage is reflected in this crop of rookies. Right fielder Domonic Brown (Phillies, age 23) has supplied plenty of power in a part-time role for Philadelphia, and the best may be yet to come. Brown fractured the hamate bone in his right wrist during spring training and is only now rounding into form. On the other corner, Andy Dirks (Tigers, age 25) has raised his profile with a hot start to his big league career, much like Detroit's Brennan Boesch did last year. Dirks won a share of the left-field job in mid-May, when Magglio Ordonez got hurt and the Tigers began to rotate players around center fielder Austin Jackson. Dirks gained admirers in spring training for his strong all-around play and then hit .328/.375/.527 in 131 at-bats for Triple-A Toledo to earn a promotion. He has the wide range of skills necessary to stay in the picture for Detroit.

ROTATION ROOKIES
Starting Pitchers

Among this group of starters, only reigning BA Minor League Player of the Year Jeremy Hellickson (Rays, age 24) was projected to open the year in a big league rotation. He's been a steady contributor to Tampa Bay's seven-strong rotation of homegrown pitchers—the others: James Shields, David Price, Wade Davis, Jeff Niemann, Andy Sonnanstine and Alex Cobb—though he has emphasized a pitch-to-contact approach this season. After striking out 9.8 batters per nine innings in his minor league career, Hellickson has fanned 5.9 per nine this season. His walk rate has spiked, too, meaning that his strikeout-to-walk ratio has slipped under 2-to-1, a discouraging trend after a 4-to-1 ratio for the Rays last season. According to Pitch f/x data available at FanGraphs, Hellickson's velocity has held steady.

Brandon Beachy (Braves, age 24) beat out Mike Minor in spring training to win Atlanta's fifth starter's gig, and all he's done is pace all rookie starters with 10.5 strikeouts per nine innings. He allows power to lefty batters (.495 slugging), but he shuts down righties, who have batted a collective .193/.250/.311 through 135 at-bats . . . With just 12 Triple-A starts to his name, lefty sinkerballer Zach Britton (Orioles, age 23) won a rotation spot in spring training, beating out Chris Tillman. [Edit: Technically, Britton beat out Tillman for the right to replace an injured Brian Matusz in the first run through the rotation.] Among pitchers who qualified for the ERA title, just seven had induced a higher rate of groundballs than had Britton, who had kept 55.6 percent of balls in play on the ground. Jake Westbrook and Charlie Morton topped 60 percent, while Jhoulys Chacin, Derek Lowe, Fausto Carmona, Tim Hudson and Trevor Cahill all lived in the same neighborhood as Britton, the only lefty on the list. A revelation through his first 10 starts (2.35 ERA), Britton slumped in late May and June, allowing a 5.35 ERA in six starts as his line-drive rate wandered north to 20 percent.

Who needs ground balls when you can blow fastballs past the opposition at 96 mph, like Michael Pineda (Mariners, age 22)? His average velocity of 95.1 mph ties Justin Verlander for tops in baseball among pitchers with at least 100 innings this season. Low walk (2.8 per nine innings) and hit (6.3) rates suggest that his control and command are just fine. A second half along the lines of his first could result in some Rookie of the Year hardware.

The most unlikely all-rookie teamer is Josh Collmenter (Diamondbacks, age 25), who relies on a deceptive overhand delivery to help his high-80s heater play up. Arizona called on Collmenter in mid-April when it placed reliever Aaron Heilman on the disabled list. He struck out 11 and walked one in 14 relief innings, which eventually earned him a spot in the rotation on May 14. Control is the name of the game for Collmenter, who has gone 3-5, 3.63 in 10 starts, which includes a rate of 2.2 walks per nine innings and a 1.12 WHIP.

Keep an eye on: Two rookie righthanders should improve in the second half as their home run rates stabilize: the Rockies' Juan Nicasio (7 strikeouts, 2.1 walks per nine, 5.08 ERA in six starts) and the Astros' Jordan Lyles (7 strikeouts, 2 walks per nine, 4.75 ERA also in six starts).

BULLPEN ROOKIES
Relief Pitchers

The Braves and Angels, contenders both, turned to classic fire-breathing rookie closers and haven't been disappointed. Craig Kimbrel (Braves, age 23) has slashed his walk rate from 7.0 per nine innings last year down to a more manageable 4.0 this year. His average fastball velocity checks in at 96 mph, so opposing managers have sought the platoon advantage frequently. Kimbrel has faced more lefties (91 plate appearances) than righties (84) this season, even though lefties have hit just .156/.267/.169 (that's 11 walks and one double) . . . With an average fastball velocity of 97.6 mph, Jordan Walden (Angels, age 23) throws harder than any pitcher with at least 30 innings this season. Opposing managers have had more success loading up the lefties against Walden, for they've hit .237/.326/.368 (.694 OPS in 90 PAs), compared with a .490 OPS (63 PAs) for righties.

Cory Luebke (Padres, age 26) proved his mettle with a strong September callup in 2010 (18 strikeouts, six walks in 17 2/3 innings), but the Padres didn't have a rotation opening until late this June. That's OK. Luebke acquitted himself to a bullpen role just fine, allowing a .183 average and boasting a 43-to-15 strikeout-to-walk ratio over 39 innings.