So you want to add an ace? Top targets and red flags

The best thing about the offseason: Every move feels big at the time, gets the juices flowing if it's your team that made the move, and makes you start dreaming of April. Then sometimes your $126 million free agent makes eight starts and wins one game.

Anyway, you want your team to add an ace this winter? Here are my top five free-agent starters and the top five trade candidates who appear to be potentially on the block. Warning: I've provided the red flags for each pitcher. Buyer beware.

Top free-agent starting pitchers

The left-hander had his best season at the perfect time, as he improved in every category: more strikeouts, fewer walks, fewer hits allowed and fewer home runs. The key was not just a better slider, but throwing it more often and getting batters to chase. His overall swing-and-miss rate of 34.7 percent tied Blake Snell for highest in the majors, and he was one of just seven qualified starters to whiff 30 percent of the batters he faced. While Corbin doesn't possess premium velocity, the total package was dominant.

The red flags: He threw a lot of sliders -- 41 percent of the time, the fourth-highest rate among pitchers with at least 100 innings. He threw his curveball -- really a variation on his slider -- another 10 percent of the time. Only Clayton Kershaw threw a higher percentage of breaking balls. Some believe throwing that many sliders increases the risk of injury, and Corbin already has a Tommy John surgery in his past. Maybe more pressing, what if hitters learn to lay off his slider? It was in the strike zone only 35 percent of the time, but Corbin induced a 46 percent chase rate.

Risk: High. Was it a breakout season or just a career peak? Reports suggest he could get a six-year contract for even more than the $120 million Yu Darvish received last offseason from the Cubs. Given the inherent risk with all pitchers, Corbin's risk profile has to be high. Front offices know this, of course, but are willing to gamble he can give them a couple of years at ace-level production and maybe a couple more decent seasons after that. I'd be wary if the money reaches Darvish-like levels.

He has been a little all over the place the past four seasons: a 2.48 ERA and Cy Young Award in 2015, 4.55 ERA in 2016, 2.90 in 2017 and then a solid season in 2018 in which he made 34 starts. Some of that is the inherent fluctuations of a pitcher who lives on ground balls and BABIP (under .270 in 2015 and 2017, over .300 in 2016 and 2018). He has a clean, easy delivery, he's in great shape and he's a tough dude who has pitched well in the postseason (3.31 ERA in 51? innings).

The red flags: Because of the movement on his pitches, Keuchel does induce weak contact, so you don't worry about the so-so strikeout rate as you might with other pitchers. Still, it can be a fine line if he loses velocity. He did have a sore shoulder in 2016 and missed time with a neck injury in 2017.

Risk: Medium. I love the competitiveness he brings to the mound. He might not have Corbin's upside, but I would prefer Keuchel at $80 million to Corbin at $130.

His great work in the postseason has made him this offseason's favored free agent -- a guy with a 100 mph fastball who throws strikes and is maybe just about to tap into his potential and won't be prohibitively costly so every team will want to sign him. His fastball always had been pretty hittable -- hard but straight -- but a cutter that he first unveiled in 2016 and amped up in 2018 (he threw it 32 percent of the time) seemed to help his four-seamer. His fastball swing-and-miss rate is 15.9 percent over his career, but it was 24.9 percent in 2018.

Red flags: Eovaldi already has two Tommy John surgeries in his past, has made 30 starts once in his career and his 3.81 ERA in 2018 is pretty much in line with his 4.16 career mark.

Risk: High. Extremely high? Still, I would love to take a gamble on him on a four-year, $60 million deal -- although with so much interest in him, the winning team might land him only with a much riskier payout.

Morton will be 35, but he's throwing harder than ever, averaging 96.1 mph on his fastball -- eighth highest in the majors among pitchers with at least 100 innings. He made 30 starts while posting the highest strikeout rate of his career, and he has allowed just 10 home runs on the road the past two seasons (compared to 22 in Houston).

Red flags: He did miss one start in late August because of shoulder discomfort and lasted just one inning with the same issue in a late-September start. Morton made one postseason start and averaged 95 mph with his fastball, but there has to be some minor concern about the shoulder.

Risk: Medium. The risk here is somewhat mitigated by his age, which means he probably won't get more than a two- or three-year contract. The Astros didn't give him a qualifying offer, so you wonder if they have their own concerns about his shoulder. Morton also had said earlier in the season that he was considering retiring. He didn't, but he might wish to sign with a team close to his wife's family in Delaware.

5. Yusei Kikuchi (28)
2018 stats in Japan: 14-4, 3.08 ERA, 163? IP, 153 SO, 124 H, 16 HR

The Seibu Lions are expected to post Kikuchi, a 6-foot lefty who throws in the low 90s and has a plus slider. His numbers were down a little bit from 2017, when he posted a 1.97 ERA and struck out 217 in 187? innings. The next pitcher on this list would be J.A. Happ, who is coming off a solid 2018, but Kikuchi is younger and could be a less expensive version of Corbin.

Red flags: He missed a few starts in 2018 with a sore shoulder and his home run rate has gone up the past couple of seasons from earlier in his career.

Risk: Medium. The shoulder issue might scare off some teams, but the top starting pitchers who have come over from Japan have fared well in the U.S., including Miles Mikolas, who posted similar numbers to Kikuchi and had an outstanding 2018 season with the Cardinals.

Trade-bait starters

Bauer refined his slider in the 2017-18 offseason and the new pitch raised his game to a new level. He led the American League in FIP and fewest home runs per nine and had a chance at the Cy Young Award until he missed more than a month late in the season with a stress fracture in his right leg. He has never had any arm issues and his analytical approach to pitching means that he is always seeking ways to improve.

Red flags: Bauer was great, but it also has been only one season of great. He also benefited from an easy slate of opponents in 2018. According to Baseball Prospectus, Bauer ranked 130th out of 137 pitchers with 100 innings in average quality of batter faced. It's also worth noting, however, that he had a 2.21 ERA against sub-.500 teams (18 starts) and 2.21 against winning teams (nine starts).

Risk: Low. MLB Trade Rumors projects an $11.8 million salary for Bauer in arbitration and that would go higher in 2020 if he has another strong season. Still, the positive health history other than the leg fracture makes him low risk for a pitcher, and I'm buying into his breakout numbers.

He finished third in the Cy Young voting as he topped 200 innings for the fifth season in a row. In those five seasons, he has won two Cy Young Awards and finished third twice. The curveball is still a wipeout pitch (.102 average allowed, 39.5 percent strikeout rate). He's under team control for three more seasons, and while the final two seasons are team options, if he's traded, his new team must exercise both options within three days after the end of the 2019 World Series.

Red flags: He wasn't quite as dominant as in 2017 and his cutter/slider in particular wasn't as consistently sending hitters back to the bench. At 33 with five seasons of heavy work behind him, there is the general concern that exists for any pitcher entering his mid-30s.

Risk: Medium. I'd almost call it low risk, as even a three-year commitment stands at $52.5 million, a bargain for a No. 1 starter. Still, you're paying the salary and giving up young talent for a 33-year-old pitcher, which increases the risk level.

After making just seven starts in 2017, Thor at least made 25 in 2018, although he wasn't quite as dominating as he was back in 2016. He blistered the strike zone with a fastball that averaged 97.4 mph and he effectively mixed in a wipeout slider, curveball and improved changeup. He has three years of team control, which perhaps makes him a more attractive trade target than Bauer or Kluber -- and also more expensive to acquire. There's the general feeling he hasn't maxed out his potential.

Red flags: Despite the top-shelf stuff, Syndergaard is ... well, more hittable than you would expect. If you combine his four-seamer and two-seam fastball together, batters hit .282/.350/.415 with a strikeout rate under 16 percent. Aside from that, there was the finger injury in 2018 and the torn latissimus muscle in 2017.

Risk: Medium. You can't ignore the injury history even as we drool at the upside. One thing I like about him, however: He does limit home runs, with just 20 allowed in 368? innings over the past three seasons. That's a big reason why he'll be a Cy Young favorite over the next three seasons. Does he get there? I'm not sure, mostly because I just don't think the movement or spin rate or whatever on his fastball offers enough swing-and-miss. But I wouldn't bet against it, either.

It's still hard to believe the D-backs signed Greinke to that six-year, $206.5 million contract, kind of a random act of impetuousness by usually conservative owner Ken Kendrick (and the then-reigning front-office duo of Tony La Russa and Dave Stewart). Greinke has been good -- 12.5 WAR in three seasons, plus another 1.2 at the plate -- but now the Diamondbacks would love to get out from under the remaining $104.5 million they owe him. They will either have to eat some of the salary or maybe include him in a trade with franchise icon Paul Goldschmidt.

Red flags: Aside from age, his average fastball velocity dipped to 89.6 mph in 2018, down from 91.0 in 2017. Of course, few pitchers change speeds and location as well as Greinke, so like a late-career Greg Maddux, he could remain successful until he's 40 and chasing a bid for Cooperstown.

Risk: Medium. He's had no major injuries in his career and his risk level is lower than most 35-year-old pitchers. He can block trades to 15 teams -- reportedly including St. Louis, one of the clubs most interested in Goldschmidt -- so trading Greinke and his salary is going to be difficult. I'd like him at $20 million per season, but $35 million is a little steep, so the D-backs are likely going to have to include some cash.

His single-season career- worst ERA is 3.37. Heck, he posted a 2.74 ERA in his last full season, back in 2016. He might be the most consistent pitcher in major league history. You know what you're going to get, and if you make the playoffs, is there any other pitcher you want starting a big game?

Red flags: He had the dirt-bike injury in 2017 and the broken finger in 2018, which is why he hasn't pitched a full season since 2016. His peripherals were noticeably down this past season, suggesting an overall decline in stuff: lower strikeout rate, lower swing-and-miss rate, higher walk rate.

Risk: Low. If he were a free agent, I'd be wary about a long-term deal, but he's pretty safe for one season. The Giants aren't likely to get overwhelmed with a huge offer, unless some team overpays for Bumgarner's postseason history. They might ultimately decide to keep him or wait until July when desperation mode might kick in -- or, who knows, maybe the Giants are actually in the playoff race and need to keep him.