Before diving in, I should probably explain what I mean by "most pivotal" since it could be interpreted in different ways. I'm referring to the one player on each team whose Fantasy value is most up in the air. It "pivots" based on factors we couldn't possibly know until the season is underway.

They're the ones for which I'm most anxious to see how things turns out, to put it another way, and I've settled on just one per team. Obviously, some teams have more candidates than others, but breaking it down this way leaves more room to argue.

And what else are we going to do?

NYY N.Y. Yankees • #30 • Age: 30
Someone is getting bumped from the Diamondbacks starting rotation at some point, and there's a chance it's Luke Weaver if he can't recapture the form that gave him the look of a breakout before spraining his UCL last May. Or, for that matter, if the injury isn't totally resolved.
ATL Atlanta • #27 • Age: 27
The author of nine home runs in 18 games before the league caught up to him last year, Austin Riley now has a chance to claim the third base job with Josh Donaldson out of the picture and wasn't nearly as vulnerable to the strikeout this spring.
BAL Baltimore • #6 • Age: 27
The bat-first prospect is sure to contribute at some point this year, possibly becoming the team's best hitter right away, but when and where (most likely a corner infield or outfield spot) will say a great deal about the way things or going for other pivotal players like Chris Davis, Renato Nunez and Austin Hays.
CHW Chi. White Sox • #23 • Age: 29
Once the top prospect in baseball, Andrew Benintendi has been in free fall the past year and a half, putting up numbers more in line with Nick Markakis. At 25, he could still turn it around, but he'll need to show early signs of it to retain any Fantasy worth.
CHC Chi. Cubs • #8 • Age: 29
It wasn't too long ago we were excited about Ian Happ as a possible 30-homer guy, and it seemed like he may have gotten the strikeouts under control down the stretch last year. Craig Kimbrel would be a good candidate, too, but it's not like there's anyone else beating down the door for that closer role.
CHW Chi. White Sox • #34 • Age: 28
The easy answer here is Luis Robert, but since his playing time status isn't really in question, I'm more curious to see what happens with Michael Kopech, who made some serious strides with his control in the weeks leading up to his Tommy John surgery and, of course, remains a flamethrower.
WAS Washington • #13 • Age: 28
Nick Senzel was such a high-end prospect that it's easy to get discouraged by what was otherwise a perfectly solid rookie performance. But if there isn't much growth in Year 2, serious doubts will begin to creep in.
CLE Cleveland • #59 • Age: 37
Domingo Santana makes for an interesting dark-horse pick, but Carlos Carrasco is of course the answer since no one can say with great assurance if he'll be back to full strength in his first season back from his leukemia battle. And yes, it's about more than just velocity readings.
KC Kansas City • #2 • Age: 29
You could make a case for Sam Hilliard, Ryan McMahon or even Brendan Rodgers, but it all basically hinges on how much Garrett Hampson plays, which partly hinges on how he performs. And the stolen base output of so many Roto GMs does, too.
DET Detroit • #48 • Age: 33
Matthew Boyd had a 3.08 ERA, 1.04 WHIP and 11.2 K/9 over his first four 14 starts but a 5.81 ERA, 1.39 WHIP and 11.9 K/9 over his final 18. He's an outlier in terms of both strikeout and home-run rate, which makes his range of outcomes especially wide.
HOU Houston • #30 • Age: 27
Surely, the Astros are ready to turn the page on Josh Reddick, especially after Kyle Tucker impressed with four homers and five steals in 22 games last September. But they've made no assurances to the 23-year-old, who had a combined 58 homers and 50 steals at Triple-A the past two years.
BOS Boston • #43 • Age: 28
Whatever strides Adalberto Mondesi seemed to be making as a hitter beginning in the second half of 2018 just completely unraveled last June -- and then he had shoulder surgery, making it so stolen bases are his only bankable contribution. But those who drafted him as a one-trick pony could be treated to an out-and-out stud if he reverses course just as quickly.
NYM N.Y. Mets • Age: 31
Dylan Bundy has a workhorse build and an A-plus offspeed pitch, which leaves me holding out hope there's still an ace outcome for the former top prospect, especially with him entering a more pitcher-friendly environment. Tommy La Stella and Shohei Ohtani both deserve honorable mentions.
LAD L.A. Dodgers • #9 • Age: 26
The left handed-hitting middle infielder who rocketed through the upper minors and up prospect lists last year had a lackluster late-season showing. With the Dodgers' unrivaled depth, he'll need to hit the ground running this time.
NYY N.Y. Yankees • #19 • Age: 34
A boring choice, maybe, given the pitchers and outfielders on the verge of breaking through for this team, but Jon Berti's 35-steals pace last year would make him a standout in that ever-so-pivotal category if he can hit enough to carve out a super-utility role.
MIL Milwaukee • #8 • Age: 40
Don't sleep on Corey Knebel giving Josh Hader a run for the closer role, but where and how much Ryan Braun plays will have a ripple effect throughout the lineup. Avisail Garcia got more in free agency than Justin Smoak did, which would suggest Braun will be primarily at first base, but if he instead remains a fixture in the right field, Garcia could end up stealing some starts from Lorenzo Cain in center.
DET Detroit • #18 • Age: 36
The Dodgers suppressed Kenta Maeda's innings in his four years with them, presumably because some of the language in his contract encouraged them to do so. The Twins don't have the same options at starting pitcher and will presumably need Maeda to be the workhorse his diverse arsenal and efficient pitch counts suggest he can be.
NYM N.Y. Mets • #39 • Age: 30
J.D. Davis' playing time is a matter of great interest, but not greater than what becomes of the closer considered the best in all of baseball heading into 2018. The Mets should know pretty early if Edwin Diaz's slider is back to form and will quickly pivot to Seth Lugo if it isn't.
OAK Oakland • #22 • Age: 29
A lot of "ifs" here, including whether Miguel Andujar will hit in his first year back from a torn labrum in his shoulder and whether he'll play mostly left field, first base or third base if he does. It'll depend both on how he adapts to those positions and how Mike Tauchman, Luke Voit and Gio Urshela are performing at the plate.
MIA Miami • #35 • Age: 29
No suspense with Jesus Luzardo -- not from me, anyway -- so I'm pinning it all on the other rookie left-hander. Coming back from Tommy John surgery presents its own challenges, but if A.J. Puk can keep his walks down, the strikeout rate should be something to behold.
PHI Philadelphia • #28 • Age: 27
The power began to show up last year for a guy who already stands out for his strike zone judgment. It's just a question of when the Phillies are willing to make their third baseman of the future their third baseman of the present.
PIT Pittsburgh • #23 • Age: 28
Mitch Keller had a 7.13 ERA in the first taste of the big leagues but had no trouble missing bats with the slider he only developed last year. He could emerge quickly.
STL St. Louis • #65 • Age: 32
My heart wants to say outfield prospect Dylan Carlson, who was pushing for a job in spring training, but my head says too much is riding on the Cardinals' closer decision and whether they'll insert Giovanny Gallegos' elite ratios into the role.
NYY N.Y. Yankees • #12 • Age: 27
MacKenzie Gore will be one of the top prospects to monitor, of course, but there's a chance he doesn't reach the majors at all in 2020. Center fielder Trent Grisham, meanwhile, hit .300 with a .407 on-base percentage, 26 homers, 12 steals and a 1.010 OPS in 97 minor-league games, and I'm anxious to see if he can come anywhere close to that as a major-leaguer.
HOU Houston • #14 • Age: 29
We know Mauricio Dubon can put the bat on the ball, giving him a chance of hitting for average. How much power he's able to generate in San Francisco and how often he'll run remain open questions, as does whether he's stationed at second base or in center field.
TOR Toronto • #16 • Age: 32
Some changes to his routine had Yusei Kikuchi throwing his fastball up to 4 mph harder this spring, leading many of us to wonder if we were too quick to write him off, but as miserable as he was in his first year stateside, he'll need to get results right away.
KC Kansas City • #63 • Age: 33
The Rays have a roster full of players whose usage we're all dying to see, and the most compelling of them, Nate Lowe, could be headed to the minors. But look, Nick Anderson might be the No. 1 reliever in Fantasy if the Rays forgo their usual by-committee nonsense and lock him in as the closer.
BOS Boston • #28 • Age: 38
How the Rangers will find at-bats for Nick Solak is a matter of some interest in Fantasy, but the range of outcomes for Corey Kluber earns him top billing here. Will he go back to being a perennial Cy Young contender, or was what we saw last April bound to continue if he hadn't fractured his forearm?
TOR Toronto • #9 • Age: 29
An unrequited sleeper last year, Danny Jansen caught renewed hype with a scintillating spring performance that was backed up by a new approach at the plate. Still, he won't get as much leeway the second time around.
WAS Washington • #8 • Age: 26
The Nationals are fully prepared to turn Anthony Rendon's third base spot over to their top prospect, but after Carter Kieboom flopped as an injury fill-in for Trea Turner last April, Fantasy players won't be won over so easily.