You'll hear an X factor used to describe the player a team needs to be good if it wants to have a good season. I don't think that gets us all the way there, because according by that definition the X factor is just the best player on a given roster. So here's what we'll do. First, players and not groups of players or traits are X factors; an entire infield can't be an X factor. Health, also, can't be an X factor; if it could, it would be the X factor for everyone. For this exercise, an X factor is one player.
To whittle things down, I've highlighted volatility. These 2018 season X factors are all volatile players. They're also all important players. They're both important and hard to predict, and I think they all have a significance that's greater than just their own roster spot. These are all players of outsize importance, who could very well make or break the season ahead. Even this definition might not be perfect, and you might think an X factor is something else entirely, but at least now I've explained the thinking behind the following picks.
Arizona Diamondbacks: Ketel Marte. Whether Marte ultimately ends up spending more time at second or short, he's going to be exciting. The team fended off trade interest in him this winter, and because of the blend of speed, discipline and surprising power, I've identified Marte as my favorite breakout candidate. What that doesn't mean is that it's going to come true. Marte fell on his face in 2016 and for all I know that could happen twice, which would trip up Arizona's intended run to the playoffs. They gave up Brandon Drury in part because they believed they weren't going to need him.
Atlanta Braves: Dansby Swanson. For all the talk about the Braves building around pitching, the young players I like the most are Ozzie Albies and Ronald Acuna. Because of those two, I can picture the Braves as a dark horse playoff team, and a rebound season from Swanson would make the picture far more promising. He turned 24 in February, and there's no giving up after one down year. If Swanson takes a step forward, the Braves could suddenly look good at several positions. And then -- especially then -- it'll be possible to see this rebuild transition into something else.
Baltimore Orioles: Chris Tillman. The O's are about to sign Alex Cobb, which relieves some pressure on Tillman. Nevertheless, I think he'll be a big deal for an Orioles team that has tried to avoid a rebuild. Before last season, Tillman was considered the ace of the staff. Thanks mostly to injuries, Tillman went off the rails in 2017. The Orioles say they've just forgotten all about it and are willing to give Tillman the benefit of the doubt. Should he recover, the Orioles could actually have enough pitching to remain relevant yet again. Then again, Tillman might be toast -- and so might be the Orioles' competitive window.