Starting pitcher Tanner Roark cruises into second after launching a double off the wall — from the eighth spot in the lineup — against the Mets on Thursday in Port St. Lucie, Fla. (Steve Mitchell/USA Today)

PORT ST. LUCIE, Fla. — The first time the Nationals’ No. 8 hitter came to bat against the Mets on Thursday night, he hit a ringing double off the left-center field wall, a short-lived argument to be moved up in the order some time soon.

But because Manager  Dave Martinez is an experimenter, and because spring training is the time to experiment, that No. 8 hitter happened to be starting pitcher Tanner Roark. Martinez said he won’t make batting his pitcher eighth a habit. This week, he has given each of his starters that chance.

For years, no one even considered hitting their pitcher eighth. Martinez admitted he never considered it a viable option as a player. But Joe Maddon often hit his starter eighth in Chicago, and Martinez saw the merits.

The Nationals’ new manager explained two main arguments for hitting his pitcher eighth, even as he suggested that when his regular, projected lineup is together, he probably won’t do it.

The first argument is that the earlier the pitcher hits in the order, the earlier the opportunity to pinch hit for him. So with a starter who doesn’t often last deep into games — a relative rarity in this Nationals rotation — his spot comes up one batter sooner.

“As I evolved as a coach and watched different things and learned about the analytics and all the information, I thought to myself: ‘You got a pitcher who in the fifth inning always has 100 pitches, why not bat him eighth?’ ” Martinez said. “This way if you have an opportunity to pinch-hit sooner, you can. If you don’t, you don’t.”

A second argument is lineup turnover. Wilmer Difo hit behind Roark on Thursday, thereby acting as a second leadoff hitter ahead of Adam Eaton. Had Difo hit eighth ahead of Roark, he probably wouldn’t have gotten many strikes to hit — why pitch to a proven hitter with the pitcher next? In theory, Difo would get more to work with in the nine spot, protected by Eaton. One could also argue that whoever hits in the seventh spot, ahead of the pitcher, will get worse pitches to hit. As Martinez explained, the whole thing depends on personnel.

Sometimes it will make more sense than others — like, he said as an example, if he decides to put Bryce Harper in the leadoff spot. He said he is considering that, too.

“So far, I like it some days. Some days I don’t,” Martinez said. “When you’ve got a guy I think is going to pitch deeper in the game, you just bat him ninth and just let him concentrate on pitching.”

Roark fared far better at the plate than he did on the mound Thursday. After three smooth innings, a series of bloops, blasts, and misplaced two-strike pitches helped the Mets score nine runs against him in the fourth. Roark was supposed to throw 90 or more pitches Thursday night, but only reached 81 before Martinez came to get him. Roark had endured an up-and-down spring before Thursday’s struggles, which pushed his spring ERA to 6.86. His next start will come against the Braves in Atlanta, and it will count.

“In my windup, everything was coming out clean and nice. I felt relaxed. Even when I came out of the game and now, I feel good. Even in that long inning, I felt good,” Roark said. “It’s just out of my stretch, the ball was up a little bit. And that’s what I’ve got to work on, just that tiny little bit of getting out in front just a little bit more, and I’ll be good.”

Because Roark’s first regular season start won’t come for 10 days, the Nationals decided to leave him in West Palm Beach — rather than flying him up to D.C. for the exhibition game — so he can get another full start in here before meeting the team for Opening Day in Cincinnati. The extended spring will also give Roark time to work from the stretch in warm weather, ideally to work out the trouble he felt Thursday.

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