They might experience several big peaks and valleys during the long regular season, but major league players often end up performing to their usual standards.
Still, a certain percentage of hitters and pitchers will either overachieve or underachieve in a major way during a given season.
Let's take a look at the player on each National League team who has most exceeded expectations, and who has been the biggest disappointment (we'll turn our attention to the American League next week).
OVERACHIEVER: He won a spring training battle for the fifth starter job, and PATRICK CORBIN has been winning like crazy ever since. He's emerged as a Cy Young candidate with his 9-0 record and 2.06 ERA through his first 11 starts.
UNDERACHIEVER: After two consecutive seasons of hitting better than .280 and knocking in more than 85 runs, catcher MIGUEL MONTERO has slumped to a .202 average, three home runs and 16 RBI. If he can revert to 2011-12 form, he could put the Diamondbacks over the top in a tight NL West race.
OVERACHIEVER: Almost literally coming out of nowhere, EVAN GATTIS held the fort as the Braves' primary catcher while Brian McCann battled back from injury. He's splitting time between left field, catcher and designated hitter these days, and he just keeps delivering big hits. He has 12 homers in his first 145 at-bats.
UNDERACHIEVER: While his brother, Justin, jumped out to a hot start for the Braves, teammate B.J. UPTON has been cold all season. He's batting just .153 and has struck out an alarming 65 times in 170 at-bats.
OVERACHIEVER: The Cubs have a couple of starting pitchers performing better than expected, but KEVIN GREGG gets the nod for suddenly turning the team's shaky closer situation into a strength. Signed as a free agent after getting released by the Los Angeles Dodgers, Gregg has a 1-0 record, is 6-for-6 in save opportunities and has a 0.59 ERA in 16 appearances.
UNDERACHIEVER: After compiling five consecutive seasons of double-digit victories, EDWIN JACKSON is going to need a big second half to make it six in a row. He's 1-8 with a 6.29 ERA.
OVERACHIEVER: The Reds had high expectations for SHIN-SOO CHOO, but he has undoubtedly surpassed them by posting a .438 on-base percentage and hitting 10 home runs from the leadoff spot. He's also done it while playing decent defense in center field after having spent most of his previous career as a corner outfielder.
UNDERACHIEVER: There aren't too many candidates here, but slick fielding shortstop ZACK COZART has failed to take a step forward offensively. If he's going to continue to hit out of the No. 2 spot in the order, he's going to need to deliver better than a .271 on-base percentage.
OVERACHIEVER: He's been a solid pitcher in the past, but JORGE DE LA ROSA had made only a combined 33 starts in three seasons since a 16-win campaign in 2009. He made just three starts in 2012 after returning from Tommy John surgery. Finally healthy, he's 7-3 with a 3.10 ERA, in line for his best year yet.
UNDERACHIEVER: The Rockies are one of baseball's most pleasant surprises, so not many names deserve consideration here. However, prior to being sidelined with a groin injury, JEFF FRANCIS had registered a 6.00 ERA through his first eight starts.
LOS ANGELES DODGERS
OVERACHIEVER: Signed to a free agent deal after starring in his native Korea, HYUN-JIN RYU figured to be a solid No. 4 or 5 starter in Los Angeles. He's been better than advertised, leading the team in wins with his 6-2 record and 2.89 ERA.
UNDERACHIEVER: His .251 average, 17 RBI and seven stolen bases aren't entirely dreadful numbers, but the Dodgers have come to expect so much more than a .335 slugging percentage from MATT KEMP. After averaging 29 homers during the last four seasons, Kemp has hit only two in 2013. He is on the disabled list.
OVERACHIEVER: Filling in for injured superstar Giancarlo Stanton, MARCELL OZUNA was called up in May after having received just 42 at-bats above Class-A ball. The 22-year-old projects as a big-time power bat. He's only hit one home run in 121 big-league at-bats, but he has held his own with a .331 batting average.
UNDERACHIEVER: Not that anyone was expecting him to be the second coming of Johnny Bench, but ROB BRANTLY projected as a catcher who would hit for a solid average and provide at least a little pop. Instead, his .222 average has been nothing special. He's also still without a home run and has a mere seven extra- base hits - all doubles - in 126 at-bats.
OVERACHIEVER: When John Axford imploded in the closer role at the start of the season, fellow Canadian journeyman JIM HENDERSON took over the job and ran with it. He's on the disabled list with a hamstring injury, but Henderson has a 2-1 record with nine saves and a 0.92 ERA in 20 appearances.
UNDERACHIEVER: Only because he possesses the talent to be an elite pitcher, YOVANI GALLARDO is the biggest of several Milwaukee disappointments. He's way too good to be just 4-5 with a 5.05 ERA. For the first time in his career, he's giving up more than a hit per inning (75 hits in 67 2/3 innings pitched).
NEW YORK METS
OVERACHIEVER: OK, MATT HARVEY was a big-time pitching prospect, so the fact that he has established himself as the Mets' ace is hardly shocking. Still, it has to be a little unexpected that Harvey would this early in his major-league career look like Roger Clemens in his prime. He's 5-0 with a 2.17 ERA. On a team that would give him more offensive support, he'd be a Cy Young Award favorite.
UNDERACHIEVER: He got off to a slow start last year and got sent to the minors. However, IKE DAVIS rebounded after his promotion and still managed to hit 32 homers. This year's start was even worse, and Davis had heard whispers that he would be sent down again. It hasn't happened, but he's hitting just .168 with five homers and 16 RBI through 173 at-bats.
OVERACHIEVER: Once a top prospect, DOMONIC BROWN saw his star dim considerably after delivering mixed results during major league stints from 2010-12. Now 25, Brown is living up to his potential. He leads the NL in home runs (17) and ranks fourth in RBI (42).
UNDERACHIEVER: His ERA is 4.86. Though not exceptionally bad, it's not nearly up to the usual standards of COLE HAMELS. Who could have possibly expected the lefty to open the year with a 1-9 record? To put it in perspective, the rest of the Phillies' staff has a 27-21 record.
OVERACHIEVER: Look up the word "journeyman" in the dictionary and it's possible JASON GRILLI will be mentioned in the definition. The 36-year-old right-hander has pitched for six major-league teams and 12 minor-league teams during a pro career that began in 1998. A major league closer for the first time, Grilli is 22-for-22 in save opportunities.
UNDERACHIEVER: There aren't too many disappointments on the overachieving Pirates, but it's starting to look like PEDRO ALVAREZ might not become much more than the modern-day Rob Deer or Dave Kingman. He has 11 homers and 30 RBIs, which is solid production, but he's batting .201 with 62 strikeouts in 169 at-bats.
SAN DIEGO PADRES
OVERACHIEVER: Because he had established himself as a top-flight defensive shortstop and base stealer, EVERTH CABRERA already possessed value for the Padres. How he's on pace for career highs in batting average (.276), on-base percentage (.361) and slugging percentage (.396) while also leading the league with 23 steals.
UNDERACHIEVER: When you pitch half of your games in a pitchers' paradise like Petco Park, a 5.35 ERA is unacceptable. Yet, that's the overall ERA that EDINSON VOLQUEZ owns, and he has actually been even worse (5.73 ERA) at Petco.
SAN FRANCISCO GIANTS
OVERACHIEVER: The Giants won a world championship with BRANDON CRAWFORD playing excellent defense at shortstop but providing minimal offense from the No. 8 spot in the batting order. He's still a standout in the field, but now he's taken a big step forward offensively, hitting .291 with five homers and 25 RBI. His OPS (on-base plus slugging percentage) is .800, which would even make Crawford an adequate middle-of-the-order hitter if he could keep it up.
UNDERACHIEVER: Before going on the disabled list with a fractured hand, RYAN VOGELSONG had posted a 2-4 record and 7.19 ERA. In 46 1/3 innings, he had surrendered 62 hits and a whopping 11 home runs.
ST. LOUIS CARDINALS
OVERACHIEVER: The Cardinals lost closer Jason Motte just before the season began, and the first man up to try to replace him struggled mightily. EDWARD MUJICA came to the rescue, though. He's 17-for-17 in save opportunities, despite being thought to be fourth or fifth in line for saves at the start of the year.
UNDERACHIEVER: How can it be anyone but the aforementioned bullpen "first man up," MITCHELL BOGGS? Sometimes successful relievers struggle with the added pressure they face when they're elevated to the closer role. Few have ever failed as badly as Boggs, who has gone 2-for-5 in save opportunities with an 0-3 record and 11.05 ERA in 14 2/3 innings. He's already been optioned to the minors twice this season.
OVERACHIEVER: Since JORDAN ZIMMERMANN won 12 games with a 2.94 ERA last season, it's not surprising he'd get off to a strong start. However, he has established himself as a top Cy Young contender on a team that boasts Stephen Strasburg and Gio Gonzalez, who garner more attention. Zimmermann is 8-3 with a 2.37 ERA.
UNDERACHIEVER: He came into the season with a torn rotator cuff in his non- throwing shoulder, and now he's hampered by bone chips in his left wrist. One has to wonder how much it's all affected DANNY ESPINOSA at the plate this season. He's batting just .158 with three homers and 12 RBIs, and his job security is waning.