The Post Sports Live crew discusses whether the Nationals are turning a corner and playing better or if it is too soon to tell. (Post Sports Live)

All baseball fans have special case studies that fascinate them because the protagonist is vivid, the plot line classic and the impact of that player on his team could be so large. One of them this year is Washington Nationals right-hander Dan Haren, who was his best self last week, dominating Atlanta for eight innings.

When Haren faces the AL champ Detroit Tigers on Thursday, it will be his seventh start with perhaps 25 more to follow. Little will be decided. But much may be inferred. In his recent starts against the thumpers of the Cards, Reds and Braves (2.84 ERA), he looked like his three-time all-star self. The Tigers’ lineup may be the toughest he sees all year. Miguel Cabrera and Prince Fielder have 69 RBI, more than the Nats’ whole opening day lineup, minus Bryce Harper. If Haren’s stuff plays against them, it may play all season.

If it does, that has major implications. Stephen Strasburg, Gio Gonzalez, Jordan Zimmermann and Ross Detwiler had a combined 3.08 ERA last season and were often considered the game’s best rotation. This year, their ERA through Wednesday night’s win by Zimmermann is 3.03.

“Reports of our demise have been greatly exaggerated — Samuel Clemens,” pitching coach Steve McCatty said.

The only anchor was Haren, who looked washed up throughout spring training and in his first three starts.

“My numbers will be where they usually are” at the end of the season, Haren vowed this week. “And if they are, the team will be in good shape because the other four guys are so good.”

After hip and back injuries sank him to a mediocre 12-13 with a 4.33 ERA last season, Haren looked like he had fallen much further. His $13 million contract might be a bust. In his first start, he gave up four titanic home runs. Who allows 26 hits in 13 innings? Haren, a 122-game winner, did. It looked like batting practice, except they don’t hit ’em that far at 5 o’clock.

Haren’s disastrous start illustrates once more how diabolically hard it is to analyze baseball, even for the players themselves. From 2008 to 2012, Haren’s average fastball velocity dipped steadily: 91.1 mph, 90.6, 90.6, 90.0. It then plummeted to 88.5 last year. After the Nats put him on winter exercises to strengthen his hip and back, Haren’s velocity this year moved back to 89.4, and against the Reds to 90.2. In summer heat, he should throw a tick faster.

How could he be so awful? Haren was a brainy, disciplined vet who used amazing control to adapt to lost speed. In 2011, pitching at 90.0, he threw one-hit, two-hit and four-hit shutouts. He won 16 games with a 3.17 ERA and pitched into the eighth inning 14 times, something Strasburg has not done once.

How could a fraction of one mph — about six inches off a fastball — make so much difference? Haren began analyzing. What he and McCatty discovered was that Haren had fallen in love with his slightly improved, but still merely serviceable fastball and was throwing it far too often: 55 percent of the time compared to 35 percent or less the past two seasons. He had forgotten that his best pitches were his cutter and splitter with his fastball best used to tease the corners. His off-speed pitches should outnumber his heat by about two-to-one, not the other way around. That was Mistake One.

It wasn’t primarily Haren’s fault. He obeyed suggestions. The Nats wanted him to throw more fastballs and work inside more often.

“We wanted to try it. He didn’t feel comfortable with it,” McCatty said. “You want to pitch how you pitch. ‘This is who I am. I spot the ball.’”

Mistake Two was that Haren, feeling healthy again, was throwing his cutter too hard on the theory that, well, faster must be better. But in his case, it wasn’t. The gap in speed between his fastball and cutter, which had been four or five mph in his best years, had fallen below three mph. In visual terms, the gap between the pitches, which had once been more than three feet, was now less than two. Hitters could look for his fastball and still adjust to his cutter. He got hit so early and often, he seldom got to his splitter.

“Stop thinking about velocity,” Haren said. “It’s felt really good.”

In his first three starts, he missed his spots and gave up an astronomical 29 line drives (yes, that’s a stat now). In his past two starts, he couldn’t have delivered the ball to the plate more precisely with forceps. He allowed just three line drives in both games combined. Can it last?

Such tiny changes hardly seem to account for the difference between an 8.10 ERA before Haren figured out his problem and 2.84 afterward. What we’ll see now, over Haren’s next batch of starts, is a test case of his theory. If it’s wrong, Haren may be headed toward the end of his career. If it’s right, as the past three starts suggest, he may be one of the season’s biggest steals.

After seven straight years as a big-time workhorse, Haren, though only 32, has something of the feel of Kevin Costner’s veteran character making one last stand in “For Love of the Game.” Haren’s never-give-up-the-ball durability may have aged him ahead of schedule. But teammates love it. When Manager Davey Johnson came to the mound in Atlanta with hot Chris Johnson at the plate as the tying run in the eighth, Haren started cussing. “I got this guy.” Johnson grinned, left him in and watched Haren strike out Johnson on four dismissive pitches, then march off.

Just three weeks ago, Haren was probably the Nats’ biggest problem.

Can such minor adjustments have such big impact? Throw fewer fastballs, more cutters and splitters. Focus on location, not speed. Live low and away, like you always have. Take a little off your cutter.

“Water seeks its own level,” McCatty said.

If he’s right, then Haren is rising.

For previous columns by Thomas Boswell, visit