The Red Sox' rotation, dismal in 2012, spent the first half of 2013 jockeying with the Tigers for the lowest ERA in the American League, and Buchholz' resurgence has been a key component of the staff's turnaround. Plagued over the first half-decade of his big-league career by injuries and inconsistency, Buchholz has seemingly resolved the latter problem by gaining better command of his arsenal and learning how to dominate opponents with his fastball, which in turn has made his excellent changeup even more effective. If he maintains those strides and the shoulder bursitis that sidelined the right-hander for most of June subsides, the Red Sox might have themselves a new ace—one who could be retained on team-friendly terms through the 2017 season. —Daniel Rathman

No pitcher had stood for consistency more than Cain, whose first seven VORPs were uniformly between 20 and 35. He'll likely come up short this season, having struggled to stay above replacement level in the first half. Cain's signature abilities are still intact—particularly his BABIP suppression, as he's aiming for a new career low while posting his fifth consecutive sub-.270 season. The exceptions: a spike in his home run rate on the road, where he has had three three-dinger starts; and with runners on base, when that BABIP has spiked to .327, leading to a career-low strand rate. He hasn't had an ERA higher than his FIP since 2006, but is in danger of doing so this year. A string of five quality starts to end June suggests he has pitched his way past this blip. —Sam Miller

Cobb went on the disabled list in mid-June after being hit in the head with a line drive, but his performance prior to the incident should not go overlooked. Cobb is another control-first right-hander from the family tree that produced James Shields and Jeremy Hellickson. His arsenal features three solid or better offerings—sinker, split-change, and curveball—each of which he's able to throw for strikes or use as chase pitches. Predictably for a groundball pitcher, Cobb keeps the ball down, and he doesn't burn himself by walking hitters. The entire package is enough to fit in somewhere in the middle of a rotation. But since this is the Rays, who have a very good infield defense, his numbers look even better than that. —R.J. Anderson

Corbin was an underdog in the competition for a rotation spot coming into the season. Now he's a slam-dunk All Star and a Cy Young contender. The left-hander has always been a guy who knew how to pitch, threw a lot of strikes, and could keep the ball down in the zone. But this year his stuff has jumped up a notch, allowing all of his other attributes to play up. Corbin's average fastball velocity has climbed by over a mile per hour in 2013, despite having spent some time in the bullpen last season. But the biggest weapon he's had at his disposal is his slider, which has become a plus-plus pitch. In fact, it's neck-and-neck with Jeff Samardzija's splitter for the pitch that induces the most whiffs per swing in the majors this year, causing hitters to look back in disgust more than half of the time. Corbin's underlying and predictive stats say he's not as good as he's been, but he's much better than we all thought he was at the start of the season. —Bret Sayre

Between PECOTA's optimistic projection—only Justin Verlander entered the season expected to out-WARP him—and his string of filthy starts at the end of last season, anything less than dominance from Darvish would have been disappointing. Consider the high hopes fulfilled. The Rangers ace has upped his velocity slightly and raised his already impressive strikeout rate by over a batter per nine innings, leading all qualified starters by a wide margin. Over the first three months of 2013, Darvish doubled his 2012 slider rate, and while he threw fewer pitches inside the strike zone, he lowered his walk rate by inducing more out-of-zone swings. If there's one worrisome sign—and you have to stretch to find one—it's his willingness to alter his approach in response to unconstructive criticism. After a seven-start winless streak provoked baseless concerns about his fastball usage, Darvish went heavy on his heater in early July, struggling in his second such start. But that's the most minor of nitpicks. This is the pitcher Texas paid the posting fee for. —Ben Lindbergh

Many observers questioned why the Marlins called up Fernandez and started his service clock in early April, but he's become the team's best story in an otherwise frustrating season. Fernandez was one of the top pitching prospects in baseball coming into the season, but 20-year-old starters aren't supposed to be able to skip both Double-A and Triple-A and put up numbers like the ones on the back of his baseball card. He's averaged nearly 96 miles per hour with his fastball this season, and he's only gotten stronger with each month that has passed. If Fernandez were to continue to strike out more than a batter per inning, he'd become only the second 20-year-old pitcher to do so while throwing more than 125 innings—though the Marlins will hope that Fernandez' career turns out better than Rick Ankiel's did. —Bret Sayre

There's no getting around the fact that Haren has pitched poorly this year, and odds are he will continue to pitch poorly the rest of the year, but a persistent optimist could dig up a few positive omens. Haren's biggest problem has been the gopher ball, due to a career-high rate of both fly balls allowed and home runs per fly ball—the latter of which is a volatile metric that could easily go down, leading to fewer runs allowed. Last year a struggling Haren was shelved for a few weeks at midseason with a sore back, and returned to pitch more effectively in the second half—perhaps this year the light will similarly switch on after his midseason DL stint. Sure, those are some slim straws to grasp at, but at this point even a slight wobble towards mediocrity would be welcome. —Ken Funck

Minor-league baseball can be a tease, giving us a glimpse of a future promise but never pulling back the curtain enough that we can see the entire stage. Harvey has been on the prospect radar for a very long time, from his amateur high school days, to his standout college experience, to his 46-start run through the minors, but very few in the game foresaw such major-league success for the 24-year-old righty. Harvey is at his best when he is facing the best; he requires the brightest lights to coerce his brightest performances. With prototypical size and frontline stuff, the right-hander has emerged as one of the top arms in the game, a must-see-TV talent who can electrify at any given moment. His command of a plus-plus fastball sets the table for his equally impressive off-speed assortment, and when you add an impressive feel for pitching and an intense competitive streak, Harvey has all the characteristics of an ace pitcher. —Jason Parks

Jackson has become one of the most consistent pitchers in the game without anyone realizing it—and that includes this year. On the surface, 2013 has been his worst season since his 2007 campaign with the Devil Rays, but the shock value of his ERA and win-loss record has obscured a career-high strikeout rate and near-career-high ground ball rate. It's the things out of his control that have been killing him. Jackson's strand rate is the worst in baseball, and he's been plagued by a high BABIP that looks even more unlucky given that the Cubs have allowed one of the majors' lowest team BABIPs. Most reassuringly, Jackson's high ERA hasn't been accompanied by a big tick down in stuff: his fastball velocity has declined only slightly, and his slider is still the same weapon it's always been, as he's gotten a better whiff percentage with the pitch than Clayton Kershaw, Yu Darvish, or Matt Harvey. It's not time to press the panic button yet. —Bret Sayre

Kennedy entered the season having allowed a .421 slugging percentage on pitches in the top third of the strike zone; this year batters are slugging a whopping 1.000 on such pitches. The culprit isn't hanging breaking balls. Sadly, it's his "rising" fastball, a signature pitch for him, but against which batters are even more lethal, posting a 1.147 slugging percentage. His flyballing, strike-throwing ways have always seemed risky in Arizona's dry air, but that's no excuse: it's actually been problems on the road that have led to his career-worst home run rate. Twelve of the 15 long balls he has allowed have come as a visitor, and he has allowed at least one in every road start but one. That's all the bad news; the good is that his fastball velocity is steady, and the rest of his peripherals haven't completely melted down. —Sam Miller

Liriano's Pittsburgh career got off to a rocky start when he missed six weeks of the season recovering from a broken arm suffered when slamming into a door to scare his kids at Christmas—the latest in a long line of head-scratching disappointments that have dogged the talented lefty's career. After making it to the mound, however, he's been lights out, finally providing a level of productivity to match his nasty stuff. Liriano has been dominant in spurts before and is prone to lose command at a moment's notice, so a half-season of solid work isn't enough to put to rest concerns about his consistency. Still, the move to the Senior Circuit—and exchanging some four-seamers for sinkers—has given him the fresh start most observers felt he needed, and as long as he throws strikes and gets grounders he'll be scaring opponents instead of his kids. —Ken Funck

Marcum's ERA has been lower than his FIP every single year of his career, so it wasn't particularly surprising to see his numbers go the other way this year. The cause was simple enough: with runners on, Marcum allowed opponents to hit .360/.403/.544, and it got even worse with runners in scoring position. With the bases empty: .238/.291/.341. It would be wrong to hold Marcum's 1-9 record, 5-plus ERA, and super-slow fastballs against him, but the best FIP of his career couldn't save him from being bitten by the injury bug again. Thoratic outlet syndrome surgery ended his season in early July. —Sam Miller

The Cardinals' ace-in-waiting at the start of the year, Miller earned a rotation spot out of spring training and sprinted out of the gate, using his mid-90s heat and power curve to overpower unprepared major league hitters. Now that he's halfway through his rookie campaign, those hitters will be much more prepared, and the young Texan will need to adjust accordingly. A few midseason struggles wouldn't be surprising, but Miller trusts his stuff enough to work in the zone, get ahead of hitters, keep his walks in check, and avoid crooked numbers on the scoreboard. So far he hasn't needed to get much mileage from his dodgy changeup, but if that becomes a usable pitch, Miller could become a perennial Cy Young candidate. —Ken Funck

The reigning AL Cy Young award winner got off to a subpar start this season, throwing his fastball a few ticks below normal and giving up more home runs than we're used to seeing before a strained triceps landed him on the DL. While any bout of injury or ineffectiveness can set alarm bells clanging, Price remains a dominant starter in his peak years with tremendous stuff and a high pitching IQ. He looked every bit the ace in three July starts, torturing American League batsman with his usual aplomb and setting tongues a-wag about how long the Rays will be able to afford him. —Ken Funck

Bad things tend to happen to pitchers who lose their best secondary offerings. And sure enough, bad things did happen to Teheran in April, as he struggled to adjust to life without his outstanding changeup. Although the reasons for the pitch's disappearance are unclear, more obvious is how Teheran made up for the loss: by tightening his slider. Never known for his breaking ball in the past, Teheran improved the pitch enough for it to function as a second above-average offering. Over 10 starts in May and June he tallied a 2.28 ERA and almost seven strikeouts per walk. Teheran isn't that good, and he's unlikely to turn into the ace people once thought he might, but he should become a middle-of-the-rotation fixture, even if the changeup doesn't return. —R.J. Anderson

Vogelsong is out until late July at the earliest after fracturing his pinky finger on a bunt attempt in May. As unfortunate as the injury is, it does serve as a useful narrative device. Vogelsong's injury is a microcosm of his season at large: no matter what he does, contact finds a way to hurt him. The crafty right-hander will never win an award for his raw stuff. Instead, he relies on sequencing and location, and when his location is bad, he gets hammered—as he did before the injury. Vogelsong won't have too many chances upon his return to prove that the location is right again. With a few more stumbles, the Giants might start wondering whether the too-good-to-be-true story of his resurgence is at its end. —R.J. Anderson