On March 6, in a spring training appearance against the Miami Marlins, Will Harris went from feeling great in the bullpen to feeling off on the mound. The switch came in a span of 10 pitches, maybe fewer, leaving Harris confused and staring at his right hand. The swelling and puffiness that had occurred in recent seasons had worsened. There was heightened pressure on his index and middle fingers. Parts of his hand were red. And that’s what made Harris, a 36-year-old reliever, bring the issue to the Washington Nationals’ training staff.

He pitched again, and it kept happening. It continued in a scrimmage against the Houston Astros. So the Nationals sent Harris to a doctor in West Palm Beach, Fla., who diagnosed him with a blood clot in his right arm. Then the team sought a second opinion and sent him to a specialist in St. Louis, who discovered that the blood clot — and the possibility of thoracic outlet syndrome — was a misdiagnosis.

The confusion set Harris back by about 20 days. He began the season on the injured list with right hand inflammation. And now, as he works back at the Nationals’ alternate site in Fredericksburg, he is learning how to pitch with some swelling and pressure in his hand. It has not gone away. It doesn’t cause pain. The plan, he says, is to limit it and limit its effect on his outcomes before he rejoins the bullpen next month. He feels a “few more weeks” is a realistic timetable. Yet he also admits that he doesn’t know.

“My body feels good; my shoulder and my elbow feel good. It’s just the hand stuff is very strange,” Harris said in a phone interview Wednesday. “We got the best doctors and best trainers in the world, and we’re all collectively trying to figure this out. But otherwise, I’m pitching, and I’m preparing myself to come back, with or without a puffy hand. Obviously hoping without, but it’s not going to hold me back from trying to pitch in major league games.”

Does this puffiness have a name?

“No, no. But if you think of one, let me know,” he said with a laugh while driving home from Fredericksburg, “That’d be great. We could diagnose this thing.”

Early Wednesday afternoon, Harris faced live hitters for the first time since he was misdiagnosed. He threw between 15 and 20 pitches and felt fine. He wasn’t at 100 percent — he expects to be in the near future — but felt only slightly hindered by the puffiness at the end of his simulated inning.

He has noticed a few things: The more he throws, the more inflamed his fingers and forearm become. That’s when the redness spreads, too. It occurs when he throws full-throttle, not while he’s just playing catch. Harris and the Nationals are experimenting with different anti-inflammatory medications. And on Wednesday, about an hour after pitching, the swelling already had subsided.

“It’s weird. The common word is weird,” Harris said. “I say it all day, every time I talk about it. You can visually see it. And you know, we’re just trying to gauge if it’s better, worse, the same, that sort of thing, through different treatments. Now that I’m actually getting on the mound and exerting myself, and putting a lot of pressure on my arm, which would bring about the symptoms, it’s a good time. Now we can try more things and see if we can alleviate some of that stuff.”

A lot of uncertainties remain. Harris, though, is hopeful this next trial-and-error phase will lead him back to the Nationals. He signed a three-year, $24 million deal with the Nationals in January 2020. In his first season with the team, he missed two weeks with a strained right groin. Yet before last summer, he had just one other IL stint in his major league career. He made 68 appearances in 2015, 66 in 2016, 61 in 2018 and 68 in 2019. And in that last year — the one that finished with him yielding a World Series-winning homer to Howie Kendrick — Harris led all American League relievers with a 1.50 ERA.

While doing so, he occasionally felt similar pressure and puffiness in his hand. Yet it only swelled after outings, and he figured it was a product of throwing so many pitches in his life. It never made him uncomfortable on the mound. It went away quickly. So he brushed it aside until, this spring, it intensified when he faced the Marlins.

He recalled feeling in “midseason form” when he warmed in the bullpen. But once in the game, he had little command or feel for his cutter and curveball. His cutter velocity was around 2 mph slower than usual. It seemed as if the power was draining out of his forearm and fingers. So he looked down at his hand, and that’s how it all began. Harris says that, because there are no past examples of this with athletes, “we are in unchartered territory.”

“I’m just preparing to pitch and do as well as I can because that’s why I’m here. That’s why I came here,” said Harris, again stressing that he will push through the swelling if it comes to that. “As long as I’m healthy and capable, then I want to be out there and I want to do my part.”

This week, as Harris inched along in Fredericksburg, Manager Dave Martinez used relievers Tanner Rainey, Daniel Hudson and Brad Hand in back-to-back wins over the St. Louis Cardinals. Rainey had the seventh, Hudson had the eighth, and Hand had the ninth. It was a simple bullpen formula that should be repeatable. But with Wander Suero on the IL with a strained left oblique and Harris still wading through his own issues, there is a chance that Hand, Hudson and Rainey could burn out.

The offseason plan was to mix the three of them and Harris in high-leverage situations. For that reason, among others, Harris can’t return soon enough.