(Jonathan Newton / The Washington Post)

As Doug Fister walked to the mound on Field 3, a coach wheeled the L-screen behind the mound.

The Nationals were starting their first sessions of live batting practice, the most baseball-like substance one can ask for in mid-February, the first time all spring hitters and pitches engage in something resembling competition. Fister was first up, and unlike most pitchers, he asked for the protective screen to be removed.

“Just because there’s something in between me and the hitter,” Fister said. “I feel like I have more of a chance of getting hit worse if I have a screen, because of a deflection off the crossbar or something else. I feel like it alters my throwing motion at times, too. So it’s one of those things I’d rather get up, go regular and have no screen.”

And so the Nationals learned another detail about their new right-hander: He is not an L screen man. Once Fister threw a couple pitches, pitching coach Steve McCatty yelled to him, “Ready when you are.”

“I’m ready,” Fister replied.

Ian Desmond dug into the batter’s box. Usually, pitchers let the hitters know what pitch is coming. But because Fister didn’t use a screen, the Nationals protected him by making hitters guess. Fister started Desmond off with two sinkers at the knees. After the second, Desmond turned and asked Ramos what pitch he had just seen. It was a sinker.

“It moved like a changeup, but with more speed,” Ramos said. “But it breaks the same. … Not too many guys throw like that. He’s very different. His sinker moves a lot. Stephen [Strasburg], other guys who throw sinkers, they don’t move too much. He didn’t throw too many hard, but his pitch is moving a lot.”

“Easy to catch,” Ramos added. “Hard to hit.”

Desmond whiffed the first two times he swung. In his second round through, he ripped a line drive into the left-center field gap. Anthony Rendon stepped in against Fister next. After he chopped one bowling-ball sinker, Rendon smiled and said, “I’ll take it.” He would smash one sinker over the center field fence, but he came away impressed with Fister.

“Nasty,” Rendon said. “He was throwing it from the sky and it’s running at your ankles. He was good. He’s phenomenal. He’s tall and lanky, but he’s fluid with it. He knows what he’s doing. He’s just so composed out there and the ball just dies the last five-to-eight feet.”

Just as Fister finished, the skies opened and players sought cover in chain-link dugouts. Taylor Jordan and Chris Young, who had just warmed up and taken the mounds, had to cut short their throwing sessions.

“I never heard of rain delays in spring training,” Nate McLouth said.

Nationals coaches switched their plan. Rather than live batting practice on two fields, they went through it on three fields. They also nixed defense; Williams plans for a full defensive session tomorrow.

“Take two, got to right,” Manager Matt Williams said. “You got to adjust.”

Players warmed up again, asked coaches where to go and scattered to their designated field. Bryce Harper walked to the cage on Field 3 and realized the first live pitcher he would face all spring would Luis Ayala, a right-hander who short-arms his pitches from a low angle and throws nothing but sinkers, changeups and sliders.

“Oh great, I get to face Ayala,” Harper said. “Sick.”

Ayala’s slop produced all manner of weak contact from a group of hitters that also included Jayson Werth and Denard Span. Ayala, signed late in the winter on a minor league deal, is one of many Nationals pitchers with a real chance to make the opening day roster.

“You get around the league enough, you spend enough time in the big leagues, you get to know yourself,” Williams said. “He knows what he can and can’t do. He’s able to change speeds well within the strike zone. Good fielder, good athlete. For me, he’s a shortstop in a pitcher’s body. He moves well. All those things contribute. He’s one of those guys who has the ability to throw it for a strike when he wants to and a ball when he wants to. And that can be effective. Doesn’t light up the radar gun. But that’s okay.”

As if facing Ayala so early in spring had not destroyed their timing enough, the group of hitters faced lefty Xavier Cedeno next. Cedeno is vying to earn a spot as the second left-handed reliever in the Nationals’ bullpen. He impressed. He dropped down to a sidearm angle and made Harper swing and miss at an inside fastball. Cedeno throws from the three different arm slots, a key to his success against left-handed hitters.

“Good arm angle,” McLouth said. “It seems like his velocity is good, too.”

On a neighboring field, Sammy Solis faced Ryan Zimmerman, Adam LaRoche and a few other hitters. He has stood out in his first major league camp. Solis may have a chance to grab one of the final spots in the bullpen, too, just one year after he finished his recovery from Tommy John surgery.

“Just coming from Potomac and hurt to being on a mound and facing the best our big league team has to offer, it was honestly a little more exciting than just going through the motions with some other guys,” Solis said.  “I felt great, man. Can’t ask for anything else. Arm felt strong. Good fastball, good location. So just got to keep working.”