The simplest explanation for Bryce Harper’s slump is that the Nationals’ celebrated rookie outfielder has worn down physically during his first season in the big leagues.

“But anyone who thinks that is old,” Manager Davey Johnson told me last week, without any hint of playfulness in his tone or expression. “That’s just old people talking, because 19-year-olds don’t get tired.”

Agreed. Lack of energy generally isn’t among the biggest problems teenagers face. Also, Harper plays baseball for a living. It’s not as if he has a nine-to-five-construction gig.

Nationals fans concerned about Harper’s drop in production since the all-star break (and judging from sports-talk radio and Internet message boards, there are quite a few of you out there) won’t find answers in studying physiology. It’s a matter of physics. Swinging too early or too late at curveballs, change-ups and fastballs thrown by the best pitchers in the world could make anyone appear to be in need of a long break. But substantial time off is the last thing Harper should get. It’s definitely not what he wants.

Harper and the Nationals are handling his unusual situation (few players Harper’s age reach the big leagues) correctly. In order for Harper to reach his cathedral-ceiling potential, he has to play. The left-handed power hitter must face the game’s toughest lefties to improve at hitting their off-speed stuff. Film study alone won’t do it. And when Harper does need an occasional day off (“For a mental break here and there,” Johnson says), Johnson will make sure he stays put in the dugout.

To succeed in Major League Baseball, players must constantly make adjustments. When scouts reveal their weaknesses at the plate, players review video of their swings to identify issues and put in extra time at the batting cage to address them. Pitchers add pitches to their repertoire and refine the ones on which they’ve relied.

Then there are the individual battles between batters and pitchers that play out during every at-bat, in every inning of every game. A pitcher may throw a knee-buckling curveball to strike out a batter — and later give up a walk-off homer to the same batter, who made a good adjustment after seeing the pitch previously in a game.

Harper is learning the hard way — and the only way — that “I have to try to be as patient as I can,” he said. “Draw my walks and not get too jumpy at times.”

Entering the four-day all-star break, Harper was batting .282 with an .826 on-base plus slugging percentage. But in 82 at-bats since play resumed, Harper, who sat out Friday’s front end of a doubleheader against the Miami Marlins, has only 15 hits for a .183 batting average. Of his nine home runs, Harper has hit only one in his last 121 at-bats. His overall batting average and OPS have dropped to .258 and .750.

“He has to figure out how they’re going to pitch him. That’s the adjustment right now,” Johnson said. From Johnson’s conversations with friends throughout the game, he has learned that opponents “have spent more time on figuring out how to pitch him than probably any other player on my ballclub.

“But he’s fine. He’s in that learning phase. Every player goes through it. Really, it’s the same thing with him and Stras [starting pitcher Stephen Strasburg]. They’re just beginning to learn where their talent fits in the league.”

To this point, Harper’s most painful lesson occurred June 16 in a 5-3, 14-inning loss to the New York Yankees. He went hitless in seven at-bats with five strikeouts and left-hander Andy Pettitte, who made his big league debut with the Yankees when Harper was two, had him twisted like a pretzel. Harper appeared as overmatched that day as Jayson Werth did all of last season. Fact is, even fully mature players go through slumps that mirror what Harper is experiencing at the outset of his career.

For the most part, pitchers are “doing the same thing they did in high school and college and little league,” Harper said. “Curveballs and change-ups and fastballs on the inside half on the hands; fastballs away, trying to get me to chase. . . . I just got to learn and bear with it.”

What was encouraging about his bad day against the Yankees, though, was that Harper didn’t take his problems at the plate into the field. He played well in center and right and made a nifty catch on a sinking line drive late in the game.

Harper’s ability to focus “will help him break out of [slumps] because no one is going to work harder than Bryce,” General Manager Mike Rizzo said recently. “Really, nothing has happened with Bryce that we haven’t expected. These are big league pitchers he’s facing. There’s a reason it’s hard to get here and stay here.”

There’s no template for developing players as young as Harper in the big leagues because most 19-year-olds in baseball work in the low levels of the minors. But Johnson is more qualified than most managers to raise Harper correctly.

During Johnson’s first stint managing in the majors with the New York Mets, pitcher Dwight Gooden was a 19-year-old phenom. Some Mets officials were actually worried that Gooden was striking out too many batters (his 276 strikeouts in 1984 are the most for a rookie in big league history).

They figured it would be better for him to throw fewer pitches in an attempt to reduce the strain on his arm, so one official suggested that the team should tinker with Gooden’s mechanics “to hit more bats” and get easier outs from popups and grounders, Johnson recalled. “I looked at him and said, ‘What? You want him to do what?’ It doesn’t work like that. You’ve got to let [players] find out who they are.”

Johnson prevented anyone from messing with Gooden’s delivery. In his second season, Gooden won the National League Cy Young Award and earned the majors’ pitching triple crown, leading in victories, earned-run average and strikeouts. Drug use derailed what once appeared to be Gooden’s fast-track path to the Hall of Fame. But by all accounts and appearances, Johnson won’t need to worry about a similar self-destruction with the well-grounded Harper.

From a fatigue standpoint, Johnson was worried about Harper playing center field regularly because of the amount of ground center fielders cover. Fortunately for the Nationals, Johnson has been able to use Harper in right, too, which requires less running, because Roger Bernadina has deserved to be in the lineup.

Bernadina is back on the bench because Werth has returned after suffering a broken wrist that sidelined him for nearly three months. Werth also is playing center to help Harper as the National League East leaders begin the final two months of their regular season — the most important stretch since baseball returned to the District. It will also be one in which the Nationals hope Harper quickly learns enough to help himself, which, not coincidentally, could help the club accomplish something unknown to Washington baseball since 1933 — reaching the postseason.

For previous columns by Jason Reid, visit