Now that it's officially 2018, we can ask what will be by far the most important question of the upcoming calendar year: Which starting pitchers are primed for a breakout season?
Last year when we did this, we said that Robbie Ray was far, far better than his 8-15, 4.90 ERA numbers in 2016 would have you believe, and he ended up finishing seventh in the National League Cy Young Award voting. We said that James Paxton's breakout had already begun, and he was dominant in an injury-shortened season. (We also said Blake Snell would be great, and he took a step back. Can't win them all.)
So, which ready-to-erupt starting arms should you be focused on for 2018? Here's five of our favorites.
Luis Castillo, Reds

Whether a pitcher has "broken out" depends largely on your perspective. With a 3-7 record in under 90 innings, it would seem that Castillo had a poor year. With a 3.12 ERA and an elite standing in a key Statcast™ metric, some might think Castillo has already broken out. Two-thirds of the nearly 550 people who responded to a recent poll said the breakout hasn't happened yet, so Castillo leads this list.
We'll admit that 89 1/3 innings aren't a large sample, and it's unusual for a 25-year-old to be on his fourth organization. (Originally dealt by the Giants for Casey McGehee, he was actually traded by the Marlins on two different occasions.) But it's what Castillo did in those 89 1/3 innings that stood out, enough so that one voter placed him third on his Rookie of the Year ballot.
Just look at where he placed among starters in three important categories:
- First in fastball velocity (97.5 mph)

• Sixth in ground-ball rate (59.7 percent)
  
• Fifth in Expected wOBA (.257)
  You're wondering what Expected wOBA is, and you can read all about it here. The short version is that it combines amount of contact allowed (strikeouts and walks) with quality of contact allowed (exit velocity and launch angle), and the first four names on the list were Max Scherzer, Chris Sale, Corey Kluber, and Clayton Kershaw. They pitched far more than 89 1/3 innings, of course, but you can't fake that kind of performance. Castillo was that good.
  Tyler Chatwood, Cubs

We actually devoted an entire article to all the ways that Chatwood looked like he had the signs of a breakout, so you can check that out here for the full details. Basically, we pointed out several reasons that made him look so appealing:
- His fastball velocity jumped from 92.6 mph to 94.6 mph

• He has elite curveball spin, and allowed almost no damage against it
  
• He had an elite ground-ball rate, with only five starters having better
  
• He's leaving Coors Field, obviously (6.07 ERA at home in 2016-17, 2.57 ERA away)
  The skills are there, though the health hasn't always been. For the first time, we'll see what Chatwood can do not having to pitch in Colorado -- and you can be sure you'll see a lot more of that curveball, which he threw just 10 percent of the time in 2017.
  Garrett Richards, Angels

Richards had a strong 2014 (2.61 ERA in 168 2/3) and a good '15 (3.65 ERA in 207 1/3), but he hasn't had that season, one that makes you think about him in terms of baseball's elite aces. That's largely due to injury; his '14 campaign ended early due to knee surgery, and he made only 12 starts in 2016-17 due to recurring elbow issues. If his '18 were to be interrupted by injury as well, it wouldn't register as a surprise.
Yet, we still hold out hope that Richards is going to have that breakout, because the talent is still there. Those 12 starts over the last two years came with an excellent 2.31 ERA, and the arm issues haven't robbed him of velocity, as his 95.7 mph fastball in 2017 was tied with Stephen Strasburg for eighth-best among starters. He's long had elite-level spin on both his fastball and his curveball, and his .273 xwOBA in 2017 was basically that of Jacob deGrom.
Throw in what ought to be an absolutely elite Angels defense -- new additions Ian Kinsler and Zack Cozart join holdovers Andrelton Simmons, Michael Trout, and Martin Maldonado -- and the only thing standing between Richards and stardom is health. The velocity, the spin, the proven ability to get Major League hitters out, that's already there.
Dinelson Lamet, Padres

A 7-8, 4.57 line for the Padres made Lamet's rookie season easy to miss, and if we're setting expectations properly here, a "breakout" for him is probably more that of "a league average starter" than it is an ace. Still, if you looked closely, there was a lot to like here, starting with a fastball that averaged 95 mph, a top-30 mark among starters.
Thanks to that fastball and a very good slider, Lamet was something near dominant against righty hitters. There were 235 starters who induced at least 100 swings from righties, and Lamet's 34.8 percent swing-and-miss rate was fifth-best -- and this is a list topped by Scherzer and Kluber. All told, Lamet's excellent line of .154/.241/.296 against righties came out to a .242 wOBA, fourth-best among starters, and just look at the other names on this list.
Lowest wOBA against righty batters, starting pitchers
.190 -- Scherzer
.229 -- Brad Peacock
.234 -- Kluber
.242 -- Lamet
.247 -- Luis Severino
.248 -- Kershaw
That's a list you want to be on. The problem, however, were lefties. Because Lamet basically only throws two pitches, he was very vulnerable to lefty batters, who tagged him for a .258/.365/.502 line. While he's working on a changeup, it's still a work in progress. If he gets there, he could be a very good starting pitcher. If not, then a potential future as a good reliever isn't a bad outcome, either.
Luiz Gohara, Braves

We thought about guys like Luke Weaver or Luis Perdomo or Walker Buehler in the last spot, but ultimately we're going to go with pure, raw, left-handed velocity. A year ago, Gohara had completed a strong year in Class A for Seattle when he was traded to Atlanta for Mallex Smith; with the Braves, he ascended through four levels and made five starts in the bigs, whiffing 31 hitters in 29 1/3 innings.
Despite making just the five appearances, Gohara showed elite velocity, finishing third on the fastball velocity leaderboard with an average of 96.4 mph, and becoming just the third lefty starter in the pitch tracking era (which dates to 2008) to throw a pitch 100 mph. (That list is now at five. The others? Paxton, David Price, Carlos Rodon, and Danny Duffy. Good company.)
So why, despite a Top 25 xwOBA that was the equivalent of Carlos Martinez or Lance McCullers, did he have a 4.91 ERA? In part because almost no other starter in baseball had a bigger gap between the quality of contact allowed and the amount of hits that found holes, which could point to poor defense or just bad luck. We'll take bets on the 21-year-old with a magical left arm finding some better fortune in 2018.