Trea Turner arrived earlier than expected in the majors, and then stuck there, turning in one of the best performances by a rookie this season. Turner finished the regular season with 13 homers, 40 RBI, a .342 batting average and .567 slugging percentage. (Pablo Martinez Monsivais/AP)

Last September, Trea Turner was called up to the major leagues to play a little, sit a lot and, on a team in turmoil, perch his skinny body and his baby face at a locker in a corner and observe. Because he arrived in a trade from San Diego and didn’t play in the minors until midseason, Turner had almost no friends in Washington.

“Growing up, whenever I got in trouble, I would do anything to get my mom to stop yellin’ at me,” said Turner, 23, who has just completed one of most electrifying half-seasons by a rookie, batting .342 with 105 hits, 13 homers, eight triples and 33 steals in 73 games. “When I got here, I was the same way. I didn’t want to do anything to get yelled at.

“I just tried to keep my head down, start making friends. When you haven’t been in an organization, it’s like a foreign locker room. It’s not easy to perform under those conditions, especially in a sport where it’s usually better if you relax and have fun.”

Turner has stunned baseball. His speed was known; he’s one of the two fastest men in the game, with Cincinnati’s Billy Hamilton. What wasn’t expected: Turner was a complete player who crushed the ball, hit a 451-foot home run, rarely stooped to bunt and lashed line drives to all fields. His instincts were so true that he switched, in weeks, from a minor league shortstop to a quickly improving center fielder because that suited the Nationals’ needs.

However, what amazed the Nats was Turner’s emergence as a person and his rise in stature and even esteem in their clubhouse.

“What’s most impressive is how far he’s come from when he got here last year. He was the quiet kid in the corner, almost painfully shy,” Jayson Werth said. “Now he is one of the best players in baseball and one of the most revered players in this clubhouse.”

Werth waited three years to sign off on Bryce Harper’s maturity. Stephen Strasburg would get it all figured out eventually. Turner? “Revered.”

“I don’t know if it’s a compliment to him or to what’s been built here that he’s come out of his shell that fast,” Werth added. “He’s always handled himself great. When he was sent down [in April], I thought he was ready. But he didn’t say a word. Then we brought him up, let him play one game [June 3]. He goes 4 for 4 [actually 3 for 3 with a walk] and he goes back down. If he was a prima donna, he might have taken that the wrong way.

“Instead, the next time he came back up [six weeks later], that had only made him blossom more. He was ready to eat people,” Werth said of the player called Triple Trea by teammates. “Ever since, it’s been obvious what we’ve got. And he’s been ready to eat.”

Pros usually judge slowly. With Turner, the Nationals formed their opinions at Trea speed. Maybe it’s the way he soaks up information. Maybe it’s the quick, comically sober home run trot.

Nationals center fielder Trea Turner safely steals second Sunday as Miami Marlins shortstop Adeiny Hechavarria is left waiting for the ball. Turner stole during the regular-season finale. Turner finished the regular season with 33 steals in 73 games. (Toni L. Sandys/The Washington Post)

“If he just matches his numbers in the minors, he’ll be an all-star and get a massive contract someday,” said Clint Robinson, one of the first Nats to befriend Turner last year. “But if he keeps playing like he has since he came up this year, he’ll be one of the best you’ve ever seen. It won’t be, ‘Who is he like?’ People will be compared to him.

“And he can get better, if you believe it. I don’t even think he has mastered the art of stealing bases yet. Now, it’s freak ability. When [coach] Davey Lopes has a whole season to work with him more, every walk will be an automatic double.” Trea might ‘come back to earth.’ He might not. But right now, he’s not missing anything.”

When Turner hears that his teammates have praised him, he beams. “I’ve heard compliments from guys on other teams. Anything small really counts from them,” he says. Someday, he’ll fill out his 6-foot-1, 185-pound frame and seem older and more serious. But right now, it is just joy and eating people alive. How will the Dodgers, and gentlemen such as Clayton Kershaw, taste?

When the NL Division Series opens at Nationals Park on Friday, the central performers will be starters Max Scherzer and Kershaw. But over the whole series, two of the most important players will be rookies — Turner and the Dodgers’ 6-5 shortstop Corey Seager, who has, with his own power-speed-glove combination, been a Turner-level performer, but for an entire season and will, as a result, be a deserving rookie of the year.

Seager has impressed everyone. But Turner made an impression on the Dodgers, too, in three games in July. He tripled twice, singled, scored three runs, drove in three, stole third and also stole home with a headfirst slide. Those were the games that forced the Nats’ hand. After that series, Dusty Baker switched him to center field and leadoff. And he’s been there ever since, knocking the socks off already high expectations.

“Yes, I did think he would be this good,” said General Manager Mike Rizzo, who traded outfielder Steven Souza for Turner and likely Game 4 starter Joe Ross in what now seems like grand theft. Rizzo did, and didn’t, see this coming. In spring training, he told me he thought Turner would be “a really good player, probably at shortstop, and make a couple of all-star teams.” That’s bold. But it also seems to fall short.

For the present, Triple Trea just feels at home, wearing a T-shirt with a huge picture of third base coach Bobby Henley on the front and, on the back, “Send ’em Short/ Send ’em Tall/ Send ’em One/ Send ’em All.” Now Turner’s reaching out to befriend minor leaguers as players such as Ian Desmond and Robinson have done for him.

“Now a lot of guys I played with in AAA are coming up, too,” says Turner, grinning. More friends. More comfort. More reasons to play the game “for fun and relaxed.”

Oh, and starting Friday, the Nats hope Triple Trea is ready to keep eating people, too.

For more by Thomas Boswell, visit washingtonpost.com/boswell.