From what any of us can tell, the American League is going to be close, and maybe closer than ever. It wouldn’t appear that there are any great teams, and it wouldn’t appear that there are any bad teams, and my favorite thing about this kind of landscape is it means a whole season could conceivably be determined by the fate of one single player. One player greatly under-achieving could knock a given team out of the hunt. On the other side of things, one player greatly improving could push a given team into first place. The closer the pack, the less it could take to emerge. That’s the theory, anyhow.

The White Sox are one of those teams you can look at and imagine 90 wins or 90 losses. Last year’s version almost got to 90 losses, but then this year’s version promises to be better and deeper. And as you get to thinking about the White Sox’s upside, you get to thinking about Carlos Rodon, who’s going to slide into the rotation behind Chris Sale and Jose Quintana. It wouldn’t be a total shock if Rodon were to struggle. But then, if Rodon were to put his skills together, that could send Chicago to the playoffs. So Rodon should be what people like to call an “x-factor,” and in thinking about Rodon, I’ve come up with two other names. One name you can link to Rodon’s signature pitch, and one name you could maybe consider as Rodon’s future.

Rodon already has 139 innings of big-league experience. The White Sox hoped he would’ve picked that experience up during meaningful contests, but instead he pitched for a floundering team. Still, that allowed Rodon to focus on his own development, and his rookie season went about as many assumed it would: good velocity, wipeout slider, inconsistent changeup and control. Rodon wound up with a sub-4 ERA, but he had to pitch around a lot of walks, and right-handed hitters would give him fits. There were highlights, and there were clear areas to improve.

As last year progressed, Rodon committed a little more to his changeup. Improving that pitch is going to be the goal for 2016. Rodon didn’t run into many problems with his slider, which has caused scouts to drool for years, but that being said, something interesting did take place. You wouldn’t have thought there was anything about Rodon’s slider he needed to tweak, but according to Brooks Baseball, little tweaks occurred. As the season went on, the slider got a little faster, even though the fastball didn’t. The slider also dropped a little less. By the last month, Rodon’s slider wound up having a lot in common with Clayton Kershaw’s.

I don’t go to the Kershaw well lightly — he’s the best pitcher on the planet, with arguably the best slider on the planet. Almost no other lefties throw their sliders as fast as Kershaw does, but Rodon could hang tight. Rodon also came close by the other PITCHf/x characteristics. Here’s a table, with Rodon’s months as a starter and Kershaw’s 2015 overall. This focuses only on sliders, showing average speed, average horizontal movement, and average vertical movement. The units for the latter two are inches.

Rodon and Kershaw Sliders, 2015 Split Speed Horizontal Vertical Rodon, May 87.3 -2.3 0.4 Rodon, June 87.3 -2.2 1.5 Rodon, July 87.0 -1.6 2.2 Rodon, August 88.4 -1.3 2.9 Rodon, September 88.2 -1.7 3.7 Kershaw, Overall 88.5 -2.0 3.8

Rodon’s slider gained about a mile. The horizontal movement didn’t budge much, but in the last column, you see a difference of more than three inches. By the end, the Rodon slider and the Kershaw slider are practically indistinguishable. There’s a gap of less than half a mile, and less than half an inch both vertically and horizontally. By the most fundamental PITCHf/x measurements, the sliders were the same.

Here are examples of what they looked like:

And here’s where they went, via Baseball Savant:

Rodon kept the slider down. Kershaw kept the slider down. Both pitchers trusted the slider against right-handed bats. And so on, and so on — it’s a conversation about two real good sliders that, in a sense, are sort of one real good slider. Rodon put his slider in good company.

What’s a little surprising about it to me is that Rodon and Kershaw have such different throwing motions, and throwing motions tend to play an enormous role in pitch behavior. Somehow, the Rodon slider still became the Kershaw slider from its different slot, and that’s pretty cool. We’ll see if it keeps up that way. The elephant in the room is everything else. Clayton Kershaw has Clayton Kershaw’s command. And, importantly, Clayton Kershaw has Clayton Kershaw’s curveball, which gives him a huge velocity range for the hitter to take into consideration. Kershaw throws his fastball at 94, and he throws his curveball at 74. Rodon throws his fastball at 93, and he throws his changeup at 85. Everything is somewhere within that narrow window.

Which brings me to the second comp. Rodon’s slider, in isolation, looks like Kershaw’s slider. But what about Rodon, overall? I mean, he could always try to learn and fold in a big curve, but so far there’s no sign of that happening. The project is the changeup, and the changeup, we’ve seen. When I look at Rodon’s whole arsenal, what I see is the potential for it to work like Francisco Liriano’s arsenal. They’re fastball/slider/changeup lefties with narrow velocity ranges, and to make it work even better, Liriano isn’t exactly a master of the strike zone. He’s figured out a way to make his approach work, and for Rodon, it could be within reach.

I’m not going to bother with another table of numbers, so just trust me on this: the pitches all look similar enough by PITCHf/x. They’re not all identical twins, but the fastballs are similar, and the sliders are similar, and the changeups are similar. There are some distinctions, but everything seems of the same family.

Last year, by pitch values, Rodon had a negative fastball, and a negative changeup. Unsurprisingly, he had a strongly positive slider. Liriano, for his career, also has a negative fastball. That’s been true even in his time in Pittsburgh. Liriano, unsurprisingly, has had a strongly positive slider. The difference is in the changeup. As a Pirate, Liriano’s changeup has come in at +0.9 runs per 100 pitches. Rodon just wound up at -1.7 runs per 100 pitches. It’s a small sample, but it supports what we already knew: Rodon’s changeup isn’t good enough yet.

He has time. He just debuted last year. Few are born with these pitches, and while many struggle with changeups for their entire careers, many others nail them down and make them reliable. What I think is encouraging is that Rodon could turn himself into Liriano even without a greatly effective heater. That’s because Liriano hasn’t had a greatly effective heater. Liriano represents an accessible upside, and upside isn’t the same as expectation, but here’s where we are. Rodon could look to Liriano as an example of what his career could be like if he figures out that changeup. It’s an elusive pitch, but it’s been successfully hunted.

The Kershaw thing? The Kershaw thing is really cool. It’s neat for Rodon’s slider to have such an incredible peer, but we sort of already knew that it would. It’s a phenomenal pitch. Rodon just needs another pitch, and he knows what it is, and he knows how to throw it. That pitch could well determine Rodon’s whole career. And in the shorter term, that pitch could well determine the fate of the year’s AL Central.