Year of the Hitter: List of sluggers ready to rise

It's a new year, and soon enough it'll be a new baseball season. As is the case each season, a new crop of stars is poised to break out in 2018. As the calendar flips to January, let's try to identify some of the hitters who could make a splash.
A breakout can take many different forms. For our purposes, we're looking for players who might be in line for an increase in offensive production in 2018 -- because of an improvement they've made, better circumstances around them, more opportunity, sustained health or even just better luck.
Which hitters will make the leap? Here are a handful of candidates.
Greg Bird, Yankees
Why: His swing is made for Yankee Stadium
When Bird first came up as a Major Leaguer in late 2015, he looked like he could become a cornerstone at first base for the Yankees. Then injuries derailed him -- in 2017, it was his ankle, and for a while his season looked to be in jeopardy. But he finally returned to the lineup in August, and he reminded fans exactly why he'd looked so promising.

Bird hit eight home runs and had an .891 OPS in his 29 games down the stretch, and he carried that momentum into the postseason, hitting three more long balls. Once he got healthy, Bird looked like a whole new hitter. His expected wOBA -- Statcast™'s metric for overall offensive performance based on quality of contact -- jumped dramatically. From his return through the postseason, it was .357, nearly 50 points higher than his .311 mark before his ankle injury sent him to the disabled list in early May. (For reference, MLB average wOBA was .327 in 2017.)
And all signs point to even better things for Bird in 2018. He's healthy, in his prime at age 25, should have a ton of opportunities in a Yankees lineup that's one of baseball's most dangerous top to bottom, and he's got a sweet lefty swing that should help to drive balls out to the right-field porch in the Bronx this season.
Byron Buxton, Twins
Why: He's putting together all his tools
Buxton is an American League Gold Glove Award-winning center fielder, but his bat finally started to come around in the second half of the 2017 season. After working extensively with hitting coach James Rowson and implementing such changes as reducing his leg kick, Buxton got the results to show for it.

Buxton's first three months of the season compared to his last three months are night and day. At the end of June, he was hitting .195/.269/.283 with four homers in 251 plate appearances. From July through the end of the season, he hit .309/.358/.538 with 12 homers in 260 plate appearances. He had twice the number of barreled balls (the most dangerous type of contact, encompassing those batted balls most likely to go for extra-base hits) -- just six before July, and 12 from July on. He increased his hard-hit rate and decreased his strikeout rate.
Buxton's elite speed is going to turn some outs into hits, and help him to take extra bases. If he can carry his second-half power into 2018, he has the potential to be a well-rounded offensive force.
Stephen Piscotty, A's
Why: His underlying numbers are better than what he had to show for them in 2017
Piscotty looked like a budding star as a rookie and sophomore, so much that the Cardinals gave him a six-year contract extension at the beginning of April. But he struggled in 2017, hitting .235 and slugging .367 with nine homers in 107 games. He spent time in the Minors, and St. Louis traded him to the A's in December. Dig a little deeper, though, and there are indications Piscotty's numbers could have looked better in 2017 and in turn could look better in 2018.

For one thing, Piscotty showed improved patience at the plate, posting a career-high 13.0 percent walk rate -- he drew one more walk in 107 games (52) than he did in 153 games in 2016. His quality of contact was also better than his results. Piscotty's 2017 wOBA was .319, below MLB average. But his expected wOBA was .337 -- if his results had matched his contact quality, he would have been 10 points better than average.
That gap was also exacerbated on Piscotty's hard-hit balls -- which he got far worse results on than in either of his previous two seasons, despite driving them in the air at his highest rate yet, where they're most likely to do damage. On his batted balls hit 95 mph or harder, Piscotty had an xwOBA of .678; his actual wOBA was .618. If Piscotty keeps hitting hard balls in the air in 2018 and that evens out, his stat line might get a nice boost.
José Martínez, Cardinals
Why: He hit everything last season
Martinez was a 28-year-old rookie and not an everyday player in 2017, but he was one of the Cardinals' best hitters down the stretch. In his 106 games, Martinez slashed .309/.379/.518 with 14 home runs; he had a wRC+ of 135, meaning he was 35 percent more productive than league average. If he could get a full season's worth of at-bats under his belt, he'd have the chance to prove what he did was no fluke.

That's far from guaranteed -- the Cardinals have a crowded outfield, and while Martinez could play first base if Matt Carpenter returns to third, St. Louis also still has Jedd Gyorko. But maybe Martinez's offense can earn him a spot in the lineup. If so, he'll be a player to watch.
Martinez's quality of contact in 2017 gave him an expected wOBA of .411, fifth best of any hitter. Only superstars Aaron Judge, Joey Votto, Mike Trout and J.D. Martinez had higher marks. (He was also excellent against multiple pitch types, including a top-five xwOBA against both four-seam fastballs and cutters/sliders.) And he wasn't just swinging out of his shoes -- 18.8 percent of Martinez's swings resulted in a hard-hit ball, the 11th-highest rate in the Majors.
Yandy Díaz, Indians
Why: He rips the ball, and hitters can learn to elevate
Diaz, like Martinez, is an "if he gets playing time" breakout candidate. The Indians have a wide range of options across the infield and outfield; Diaz is an option in the corners, but it all depends on how Terry Francona aligns the defense.

The 25-year-old got his first career action in 2017, and his stat line was underwhelming -- Diaz had a wRC+ of just 86 in his 179 plate appearances, and he didn't hit a single home run. So why think he might be on the verge of bigger production? Well, in his limited at-bats, Diaz had one of the highest hard-hit rates in the Major Leagues -- 50.8 percent of his batted balls had an exit velocity of at least 95 mph, fifth-best of any hitter. And 22.1 percent of his swings resulted in a hard-hit ball, the highest rate in the game.
But all those hard-hit balls yielded a wOBA of just .448, the lowest of any hitter on hard-hit balls. (Across MLB, the wOBA on hard-hit balls was .706.) The problem is that Diaz hit way too many grounders. Of his hard-hit balls, 56.5 percent were on the ground, third most of any hitter. Those aren't going to do damage. Diaz needs to learn how to elevate. If he can join the air ball revolution, he'll be dangerous.
David Dahl, Rockies
Why: Coors Field, plus his rookie showing
Dahl is a big wild card because of his health -- he missed the 2017 season with a stress reaction in one of his ribs, playing only a handful of Minor League games before being shut down at the end of July. But he tweeted early in December that he is healthy and ready for Spring Training, and the Rockies' corner outfield is open with Carlos González hitting free agency. If he is indeed ready to go in 2018, Dahl could be a prime breakout candidate.

Dahl was impressive when he debuted for the Rockies in 2016, slashing .315/.359/.500 with seven homers in his 63 games. He did benefit from unsustainable batted-ball luck -- Dahl's batting average on balls in play was .404 -- but that doesn't mean he won't hit when he comes back. Dahl had a line-drive rate of 31.3 percent, for example -- ranking 21 out of the 325 hitters with at least 150 batted balls in 2016 -- and line drives, naturally, are the type of batted ball most likely to result in success for the hitter.
He's also still just 23 years old, and was a highly touted prospect when he came up, ranked third in the Rockies' system and 47th overall in MLB in 2015. The other major factor: his home stadium. Coors Field is the best place to hit in the Majors, and it seems like every season there's a new Rockies hitter breaking out. If he's healthy, that could be Dahl in 2018.