We are in an era when conventional wisdom is being tested like never before, with players tinkering and experimenting at unprecedented levels.
The most dramatic example is perhaps the second act of pitcher Rich Hill, his late-career comeback fueled by pivoting away from the traditional notion that the fastball must be the primary pitch. Hill's primary pitch is his best pitch, the curveball. Others have followed pitch-tracking technology, which is giving them the hard data to influence what pitches they use how often and changes in their pitch sequencing.
While some breakouts on the mound will still follow a more traditional route --a young talent maturing and better harnessing his stuff, for instance -- others will use data more and more to test conventional thinking and experiment. Which means that we might be in an era of more breakouts.
With that in mind, let's examine the pitchers who might have the stuff, or curiosity -- or both -- to reach another level in 2018, even ace-hood.
Aaron Nola, Philadelphia Phillies: Nola already has broken out by becoming a quality rotation option, posting 4.3 fWAR (FanGraphs' WAR) in 2017 with a 3.54 ERA and 3.27 FIP. He has a signature pitch, a whiffle-ball curve that limited opponents to a .172 average and .259 isolated slugging mark last season. That one pitch ranked No. 1 in horizontal movement among all curveballs last season (9.69 inches of movement to the glove side), according to the Baseball Prospectus leaderboard. Ranking Nos. 2 and 3? Adam Wainwright and Hill. The pitch was worth 18 runs above average, according to FanGraphs' linear weights. Not only does it miss bats, but like Hill's curve, it often jelly-legs batters for called strikes.
But Nola is ready to take another step, perhaps toward ace status. He could follow the Hill path and simply increase the number of curveballs he throws. Or he could add a third plus pitch, which he already may be doing. Nola doubled his changeup usage last season, and the pitch was slightly above average, according to FanGraphs' linear weights (rating two runs above league average). The pitch helped him improve the second time through the order when he was actually better (.618 opponent OPS) than his first time through (.706). He has thrown more quality changeups this spring, featuring arm-side fade from left-handed batters.
Nola generates swing-and-miss results and ground balls, and he limits walks. He might improve in all three areas in 2018. He might be ready to lead a contending club's rotation. While he has already broken out, there's more here.
Trevor Bauer, Cleveland Indians: The Indians' rotation is already loaded. Their staff made history last season when it became the first group to strike out 10 batters per nine innings for a season in major league baseball. Corey Kluber and Carlos Carrasco are elite rotation options. And Bauer might be ready to join them.
Bauer was one of the worst pitchers in baseball entering the final day of May 2017, when he ended the month with the highest ERA in the majors (6.00) among qualified pitchers. Then on May 30, he made a dramatic change in his approach -- he began throwing his best pitch, the curveball, at near-Rich Hill levels. He struck out 14 Oakland A's that afternoon and then struck out 102 in 95 innings through the rest of the season. He simplified his pitch mix in June and July and then began throwing a slider -- and lessening his cut fastball usage -- at the end of July. He used the slider to get a 20.3 percent swinging strike rate, and it rated as an above-average offering.
He has spent the offseason working to improve the slider, studying the game's best and vows to have it become another plus pitch. In the second half last season, Bauer ranked 18th among starting pitchers in WAR (f1.8) to go along with a 3.01 ERA and 3.68 FIP. With a new slider he might be ready to pick up where the left off and reach another level.
Blake Snell, Tampa Bay Rays: On the surface, Tampa Bay's best pitching prospect appeared to have a pedestrian first full season in the majors last year. But according to research by FanGraphs' Jeff Sullivan, Snell enjoyed the second-greatest improvement in expected wOBA in the second half, dropping from his earlier figure by 83 points. The only pitcher who bettered him was Justin Verlander (84 points). What that means is that Snell allowed much weaker contact in the second half.
Snell has an ideal variety of pitches, featuring a mid-90s fastball, changeup, slider and curveball. He threw all pitches with a double-digit usage rate, uncommon variety for young pitcher. And his secondary pitches all had whiff rates of 20 percent or greater.
Not only did his quality of batted balls improve as he allowed much weaker contact in the second half but also his ability to miss bats and avoid walks. In the first half, the lefty posted a 19.2 percent strikeout rate and a 14.5 percent walk rate, which showed a troubling lack of command. But in the second half, he increased his strikeout rate to 23.7 percent and cut his walks to 8 percent. It fueled an improvement in FIP from 5.14 in the first half to 3.56 in the second. His swinging strike rate climbed to an elite 12 percent in the second half.
The most obvious change Snell made was moving from the right side of the rubber to the left while also apparently raising his release point. Sometimes it's as simple as making a rather subtle adjustment to unlock elite stuff, which Snell possesses. The Rays will need him to be effective because they plan to implement a four-man rotation and are already down Brent Honeywell and Jose De Leon, who both had Tommy John surgery this spring. Snell is so good he could push Chris Archer for ace status this season.
Kevin Gausman, Baltimore Orioles: It might seem that the Orioles have failed to developed a pitching prospect in the 21st century, with their litany of failures, and many might include Gausman among them. He has produced a middling 4.18 ERA and 4.08 FIP since being selected fourth overall out of LSU in 2012. But we live in a baseball era in which players are extracting more value out of themselves through experiments in the form of swing changes and pitch usage. Gausman began to change what he threw last season and enjoyed much better results.
Over his final 14 starts, Gausman posted a 2.70 ERA and 9.5 K/9 and 2.8 BB/9 marks, near acelike rates. This might not be a small-sample-size fluke since it was fed by an increase in his split-finger fastball usage. He threw the pitch 23.4 percent of the time during that stretch, which would represent a career high for a single season if extrapolated out over a full season. He essentially shelved the curveball, and for good reason.
Gausman's splitter led all of baseball with negative-9.15 inches of horizontal movement, more than a full inch greater than No. 2-ranking Alex Cobb's (negative-7.85 inches). He should throw the pitch more because opponents have hit just .200 against it for his career and slugged .329. Last season opponents batted .204 against the pitch; by comparison, they hit at least .302 against his other three offerings.
Gausman has a potentially elite pitch; it has been underused, but maybe that's about to change. One thing is certain -- the Orioles desperately need Gausman to make a leap in his performance level.
Lucas Giolito, Chicago White Sox: Giolito is the youngest and longest shot on this list to join the ranks of the elite arms in 2018, but he too has made a dramatic change that could allow his stuff to play up.
As Jeff Sullivan noted at FanGraphs earlier in March, Giolito has lowered his arm slot this spring, which has helped improve his fastball command and velocity. His curveball has been a fall-off-a-cliff offering, perplexing opponents in Cactus League play. While it's folly to make too much of spring training performance, it can mean something if a player is going through a major mechanical adjustment. In four straight starts entering Sunday, Giolito has allowed just 11 hits, 4 runs and 4 walks over 17⅔ innings in the arid, hitter-favorable environment of Arizona. He has struck out 17.
Sometimes it can be something as simple as dropping an arm slot, like James Paxton did several years ago with the Mariners. Sometimes it can be switching sides of the rubber, or shedding the windup as Carrasco and Alex Wood have done to great success. Giolito has the physical gifts to be an ace. He was touted as a potential top-five overall pick out of high school in 2012 until an elbow injury. Since entering pro ball he has endured dramatic swings in performance, but he might be ready to help accelerate the White Sox's pace on their road back to relevance.
Jon Gray, Colorado Rockies: Denver and Coors Field will always inflate traditional numbers, but Gray posted the 11th-best FIP mark in the majors last season (77). He has developed a third pitch -- an above-average curveball -- to go with his mid-90s fastball and wipeout slider. He has posted two straight 3.0-plus fWAR seasons. What he hasn't done? Stay healthy, posting innings totals of just 168 and 110 the past two seasons. If Gray can stay healthy, he'll be a bona fide No. 1 and earn the reputation -- and WAR total -- of an ace.
Sean Manaea, Oakland Athletics: Throw out Manaea's 2017 numbers, as he dealt with a shoulder strain and illness that robbed him of 20 pounds. He was rarely 100 percent. Even with the health issues, Manaea's slider generated whiffs per swing at a 40.3 percent rate, and his changeup recorded whiffs at a 37 percent rate. Manaea's slider held opponents to a .168 average. His fastball velocity varied, but he averaged 92 mph from the left side. With a full year of health, Manaea could hone his command, enjoy a velocity bump and execute two plus pitches. Few lefties possess his assortment of gifts. If he stays healthy, he might be close to putting it all together.