Mark Appel is one of the great unknowns this spring. He remains something of an enigma, wrapped in a riddle, and now shrouded in post-surgery mystery.

I will begin with a brief history of a player who has seen his prospect luster diminished as dramatically as few pitchers in recent memory.

Recall that the former Stanford University ace was drafted twice in the first round. In 2012, under the new restrictions on amateur signing bonuses, the Pirates weren’t willing to forfeit a future draft pick for exceeding their pool limit. Appel’s signing demands were not met, and he returned to Stanford.

He returned for his senior year, which seemed like a risky decision given that injury or poor performance could diminish his stock. But Appel won the bet on himself as he was drafted No. 1 overall in 2013, by Houston, one spot ahead of Kris Bryant. While Appel over Bryant looks like Bowie-over-Jordan-like decision at the moment, Appel had an impressive resume coming out of school, including a mid-90s fastball and wipeout slider that helped him set the program’s strikeout record with this very pitch against UCLA nearly four years ago:

But few have fallen further than Appel in the last four years.

On both the MLB.com and Baseball Prospectus top 100 prospect lists, Appel’s ranking declined each year from 2014 to 2015 to 2016 — until this spring, when he’s fallen off the lists completely. He wasn’t ranked in the Baseball America preseason top 100 last year. He has a 5.04 career ERA in the minors. Less than three years after being selected first overall, he was traded by the Astros last winter — along with Vince Velasquez — for right-handed reliever Ken Giles as part of a seven-player deal.

In 2016, in his first year with the Phillies, he made just eight starts while dealing first with a shoulder issue and then surgery to clean out bone spurs from his right elbow. And, of course, the man picked after him in 2013 was named the NL MVP last season. Appel appeared to be hampered not by just health, but by the pressures of expectation and comparison.

Wrote Peter Gammons in January:

“It has not been an easy four years for Appel. He is shy, as well as very smart, and has always been faced with expectations; Houston is his home town, Bryant was clearly headed for stardom.”

Now, the 25-year-old Appel is ranked as the Phillies’ No. 25 prospect by FanGraphs prospect analyst Eric Longenhagen. Wrote Longenhagen:

“I don’t know what the hell to do with Appel, who at times looks like a good mid-rotation arm and at others looks like a total non-prospect. Those instances can both occur within the same start.”

Appel has been one of the sport’s great mysteries: at 6-foot-4, 225 pounds, he has the perfect pitcher’s build. He has mid-90s fastball velocity when healthy, what at times is graded as a plus slider, and a changeup. Yet, it’s never added up to results.

Given Appel’s dramatic fall in the prospect world, it’s interesting to see that a different player has arrived to Phillies camp this spring in Clearwater, Fla. In an excellent profile on Appel, the right-hander told Ryan Lawrence of PhillyVoice.com that his delivery, health and mindset are all in a better place:

“I think a big thing for me, and really pitchers in general, is the amount of extension you get when you’re throwing the ball,” he said. “I think it helps with velocity, it helps with control, it helps just with the stress that goes through your elbow. When I had bone spurs, it really limited that range. I really physically couldn’t get that full extension. And now through the rehab process, I’ve been able to increase my range of motion. … The last two bullpens I’ve thrown is probably the best I’ve felt since before the surgery.”

Lawrence recounts how Appel also showed up to camp with the Bible verse “Romans 12:2” embroidered on his black Mizuno pitching glove, and a Bible app downloaded on his phone, which he consults before taking the field. This is a player looking for perspective amid disappointing results. Said Appel to Lawrence: “For me, there is no reason ever to not be hopeful in all circumstances, no matter how bleak things may look. Keeping it in perspective, things have been bleaker. “

The rebuilding Phillies enjoyed a number of contributions from promising arms last year from Aaron Nola, Jerad Eickhoff, Zach Eflin, Jake Thompson and, of course, Velasquez, yet another player to whom Appel will be linked along with Bryant.

While he might be running out of time and chances, he’s physically healthy and perhaps in a better place mentally. This might be one of those “best shape of life” stories that actually means something. Perhaps he’s simply taking a Homer Bailey-like circuitous route to the middle of a major-league rotation. With the Phillies’ rebuild still under construction, the club can be patient with him before considering him for a relief role, which is often the last recourse with any failed starting pitching prospect.

In an era with so many young stars emerging at the major-league level, Appel seems close to being forgotten. But he deserves another look. Even if he’ll never be the top-of-the-rotation arm some thought he could become, there is still time for him to emerge as another piece to the Phillies rebuilding efforts. And perhaps it’s being out of the spotlight, being out of Houston, being somewhat forgotten that will allow him to begin to fulfill some of his promise. There’s the baseball axiom that states a club should never give up on a young arm, and Appel might put that to the test. But he could still be worth the wait.