2015 was deservedly known as “The Year of the Prospect.” Elite talents reached the big leagues, made impacts, and graduated from prospect lists. In fact, 25 of Baseball Prospectus’ top-50 prospects reached the big leagues, and nearly all of them were there for more than just a cup of coffee. Baseball’s youngest stars began to carve out names for themselves in today’s game, with the most notable including Kris Bryant, Fransisco Lindor, Carlos Correa, Addison Russell, Michael Conforto, Miguel Sano, Noah Syndergaard, Kyle Schwarber, Eduardo Rodriguez, and Roberto Osuna. Among this group of impact performers, there’s a slew of consensus elite prospects, and then that final name: Roberto Osuna. Given the context, Osuna was arguably the most impressive of all players, despite being far from the biggest name. What he did in 2015 was virtually unheard of, and Osuna deserves much more recognition, both amongst fantasy circles and throughout all of baseball.

On the dominant Toronto Blue Jays squad, one of the most valuable players came from where you would least expect it. When the 19-year old Roberto Osuna joined the Blue Jays in Spring Training, it didn’t make much news. As the case with many other young prospects, it seemed Osuna would only spend a week or two in big league camp before leaving. It was practically set in stone that, no matter how Osuna performed, he would get a couple of relief innings before returning to where he finished 2014: High-A. Expectations were low for the young righty—he wasn’t just the youngest player on the Blue Jays in camp, but the second youngest player in all of Spring Training. Osuna was preparing for his first full year back from Tommy John surgery, and had a 6.55 ERA in seven starts at High-A the year before. But, something remarkable happened. In Osuna’s first relief appearance, he went one scoreless inning. In his second appearance, he went two perfect innings. In his third—two more scoreless innings. In his fourth chance, the Blue Jays gave him the start and Osuna went 3.2 scoreless innings. All the sudden, it was March 22^nd, and Osuna was still on the Spring Training squad. And he hadn’t given up a run. His next appearance was a perfect one inning, in which he struck out the side. Finally, there was some talk about Osuna: would the Blue Jays have the audacity to carry a teenager in the bullpen?

Flash forward to a rainy April 8^th. The Blue Jays are down by one run in the eighth inning, with the bases loaded and the heart of the Yankees order up to bat. Osuna is called in to face Alex Rodriguez, and manages to strike him out. Next up is Chase Headley, who hits a pop up to Jose Bautista to end the inning. Although Osuna was buried on the Blue Jays’ bullpen depth chart, he had his foot in the door following an exciting major league debut. This appearance marked the start of Osuna’s role as the best pitcher in the Blue Jays bullpen. He had a 1.38 ERA in fifteen April innings, and a 2.13 ERA in 12.2 May innings. Osuna continued with an incredible run, soon taking over the closer’s role and throwing 69.2 innings of 2.58 ERA ball, along with 20 saves.

So why did I spend all that time talking about the first two months of Osuna’s career? It’s important to know his background, because his remarkable season goes beyond statistics. Sure, Osuna had the most WAR for a relief pitcher under 21 since 1972, but the context of his season is vital. Osuna went from a 6.55 ERA in High-A—coming off of Tommy John surgery—to throwing in the big leagues. Osuna had just 22 innings above Rookie Ball the past three seasons, but was the best reliever on the Blue Jays. Not only does this information make his season all the more impressive, but it alters how he should be valued in fantasy leagues as well. Osuna’s a rare breed in fantasy…he’s a pitcher who could be immensely valuable as a closer, but also someone who has major upside as a starter. This is extremely intriguing, but also confusing. It’s a challenge to figure out how to value a player like this, and what to expect from him in 2016.

As mentioned, there are two sides to Roberto Osuna, the relief pitcher and the starting pitcher. Let’s start with the reliever. Out of the bullpen, Osuna features a plus heater that he can throw as either a four-seam or two-seam fastball. The pitch has a whole lot going for it, from the average velocity of 96.33 mph (44^th in the MLB) to its 27.72% whiffs/swing rate (27^th in the MLB). The pitch isn’t a straight pitch either, with nice rising action. It wouldn’t have been surprising for the fastball to lose some velocity over the course of the season—given the large bump in workload and that it was Osuna’s first full year back from Tommy John surgery—but that was far from the case. Naturally, Osuna defied expectations and actually saw his fastball velocity rise, from 95.52 mph in April to 96.89 in October. What’s important isn’t that he increased his velocity—that may not mean anything—but that his velocity didn’t fall off. Osuna’s also shown the ability to bump his fastball up a couple more miles per hour when needed, and his season high velocity was 99.4 mph.

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Osuna also features two very solid secondaries that he utilizes relatively equally in his changeup and his slider. The more effective of the two—his changeup—actually isn’t anything special movement wise. But, Osuna has shown the ability to spot the pitch and use it in tandem with his fastball. That is the key to his changeup: the absurd 13+ mph difference it has from the heater. As a result, the changeup is 52^th in the league in whiffs per swing and has proven to be a challenging pitch to square up for hitters; opponents have mustered a mere .129 slugging percentage off the pitch.

Osuna’s third pitch is a slider, which he throws 15.2% of the time. While it hasn’t generated the results of his changeup (it has a .256 SLG), the slider is an impressive offering nevertheless. It generates swings and misses at an elite rate, 16^th best in the majors, and the pitch’s average velocity of 88.52 mph is 20^th highest in the majors. Osuna also ramped up his usage of the slider as the year went on, showing increased faith in the pitch.

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The slider could surpass his changeup as the better secondary pitch, but at his best Osuna features three plus pitches. The pitches work very well together, as the fastball and changeup benefit from one another and all three have distinct velocities. Osuna’s one weakness is his lack of groundballs. The 20-year old’s fastball induces groundballs at about the league average rate, but his other two pitches aren’t as good at keeping the balls on the ground.

As a closer, this may not be the end of the world; Osuna’s ability to make batters swing and miss at such a high rate can nullify his 34.3 percent ground ball rate, which is well below the league average of 45.3 percent. But, can he succeed if the Blue Jays choose to give him a chance as a starter?

Here’s where things get complicated for Osuna and his fantasy stock. The Blue Jays have kept quiet about their plans for Osuna next year. Earlier in the offseason, there were whispers about stretching out Osuna for 2015, and ex-Blue Jays General Manager Alex Anthopoulos saw Osuna as a starter long term. With the new regime in, though, things are tougher to decipher. Still, some offseason moves can help to figure out the prospect’s place. The Blue Jays retained J.A. Happ and Marco Estrada, while also trading a good reliever in Liam Hendricks for Jesse Chavez. A couple of days ago, it seemed that the improved rotation and weaker bullpen would force Osuna to stay as a reliever, but Friday’s trade of Drew Storen for Ben Revere flips things on its head. Now, the Blue Jays can afford to move either Osuna or Aaron Sanchez—a player in a similar situation to Osuna—to the rotation thanks to new depth.

Even more intriguing, the Blue Jays have been open to moving R.A. Dickey, so that too would clear up a spot in the rotation for one of the young pitchers. Sanchez has already gotten a chance in the rotation and struggled. He seems to be better suited as a high-leverage reliever in the future, but Sanchez wants to be a starter: even training as one this offseason. Sanchez also wouldn’t need time in the minor leagues to shake off the rust and become a starter again. Although Osuna has more upside in the rotation and is probably more valuable as a starter, he would need time in the minor leagues before being major league ready. It seems that the Blue Jays could make a choice between stretching out either Osuna or Sanchez. The team may not want to mess with a good thing in Osuna as their closer, and there’s the risk of ruining him (a la Joba Chamberlain or Daniel Bard) if they move the young pitcher back and forth from the rotation to the bullpen. Still, Osuna as a successful starter is significantly more valuable than Osuna as a successful closer, so it may just be a matter of time before he gets a chance in the rotation.

Starting pitcher Roberto Osuna is a very interesting idea to entertain. As previously mentioned, he throws three plus pitches while also mixing in a two-seam fastball. But, there’s a couple of risks that need to be addressed with Osuna as a starter. The first of which being is the potential for pitch regression in longer stints. It’s been seen plenty of times—a pitcher in shorter bursts has much more dominant stuff than when he works out of the rotation.

Another obstacle is that Osuna has thrown both too many and too few innings. In 2014, fresh off of Tommy John surgery, he threw just 35.1 innings. This is a perfectly appropriate number for a very young pitcher coming off of a major arm surgery. Things get a bit scary when you look at last year’s innings for Osuna, when he threw more than twice as many innings at 78 frames (including the postseason). This isn’t the most egregious increase ever, but the Blue Jays may be best served taking it slowly with an innings increase next season. If they stretch him out, he would throw even more innings which could turn into an issue.

Osuna had a heavy workload last year, but the experience wasn’t enough for him to be ready as a starter. Certainly, Osuna is a remarkably advanced pitcher, but he’s also yet to work as a starter since undergoing Tommy John surgery. While he technically made eight starts in the minors last year, Osuna averaged under three innings an outing and was pummeled in High-A). Before undergoing Tommy John surgery, Osuna had made just 15 starts between Short Season and Low-A. Those starts were barely over 4 innings on average, and his 4.79 ERA in those outings weren’t very comforting either. Osuna’s grown in his time with the Blue Jays’ bullpen, so he wouldn’t need two to four years in the minors to develop like a normal prospect of his age would, but the pitcher will still need time to adjust to starting. At the very least, a half-season in Double-A or Triple-A would be required. In addition, it would take Osuna several seasons to work up to a normal starter’s full season workload. Then again, he’s just 20, so it could take Osuna four years to become a full-blown starter and he’d still be very young.

The Blue Jays have good reason to wait some time before making Osuna a starter. They don’t have a need in the rotation like they do in the bullpen, and the team also has a window of contention that won’t last forever. It may be smart to extract value out of Osuna now, and ‘waste time’ with him in the minors in a couple seasons when the team may be retooling. Still, making Osuna a starter is a very intriguing prospect. At just 20, Osuna’s flashing three plus pitches, and that could lead him to being a second or third starter in the rotation. As Osuna develops more and moves further away from Tommy John surgery, his likelihood of reaching that ceiling, if given the chance, increases.

Despite the obvious payoffs that could occur if Osuna moves to the rotation, he’s still a very valuable player. There’s no reason why Osuna can’t improve upon last year’s campaign if he remains a reliever—he could become a dominant shutdown closer with very high strikeout numbers. The biggest thing that could hold Osuna back next year would be flyballs, as that may make him homerun prone—never a good quality for a closer. Still, these groundball rates may increase as Osuna’s sample size increases and he gains experience, as it often takes time for groundball rates to stabilize.

While there’s a chance that Osuna also loses his closing gig to Drew Storen, it’s not the biggest cause for concern. There are a few scenarios that could occur, but if Osuna is kept in the bullpen he should have the edge for the closing job. It may make sense to have a competition between him and Storen, but if the Blue Jays want to keep Osuna in the bullpen, it wouldn’t make much sense to remove him from the closers role. Going into next season, fantasy owners will need to value Osuna highly but cautiously. A truly nasty pitcher with ice water in his veins, Osuna has the talent to be a top-tier closer next year. Still, he could lose the closers role, making him relatively useless in fantasy for the short term. But at just 20, he becomes a coveted fantasy option long term, whether as a starter or as a closer (Storen has just one season left of team control, so Osuna wouldn’t be dethroned from the closers gig for long). The fact remains that Osuna has a very special dynasty profile. There’s a good chance he’s a top closer, and even better, Osuna could be a very good starter. Even the scenario where Osuna fails as a starter would turn out fine, as a shift back to being a dominant reliever isn’t bad at all. The downside to Osuna is minimal and the upside is immense, making him an ideal player to own in fantasy leagues.