Sometimes, you just know. At age 16, Bryce Harper appeared on the cover of Sports Illustrated, with the caption boasting of his 570-foot home runs (and 96-mph fastball). A year later, he was the number-one overall pick in MLB's amateur draft. Two years after that, he was mashing big league pitching. He was The Natural.

Nolan Arenado was a good prospect himself coming out of high school. He hit .456 in his junior year and .517 in his senior year at El Toro High School in Lake Forest, California, made the Los Angeles Times All-Star team, and earned high marks from scouts for his bat.

Still, the rest of his 2009 draft scouting report was ... not kind. Listed at 6'2", 200 pounds, Arenado was viewed as a somewhat bad-bodied, not-very-athletic prospect. Under baserunning, the report read, "It's not a part of his game." Under running speed, "He's duck-footed and lumbers."

More than just his baserunning and foot speed, the prevailing concern over Arenado's future was which position he would play in pro ball. Primarily a shortstop in high school, he'd also done a little catching. Thanks to his strong throwing arm and less-than-chiseled physique, multiple teams projected him as a future catcher. In his MLB scouting bureau video, we see a thick-bodied hitter roping line drives in batting practice, followed by Arenado gunning a bunch of throws to second from behind the plate. It's only toward the end that we he see him at shortstop, making impressive throws, but looking like something less than the second coming of Ozzie Smith.

Seven years later, that scouting report looks like it was written in Sanskrit. Now 25 years old, he looks lean and athletic in his Rockies home whites. Though he won't compete for basestealing titles, he's roughly a league-average baserunner by advanced metrics. Once a good hitting prospect, he's now an absolute terror at the plate, combining elite contact skills with light-tower power. He long ago gave up on shortstop and catcher aspirations to become a full-time third baseman, where his combination of superior instincts, impressive agility, and that rocket arm have earned him compliments from Brooks Robinson -- who's merely the best defensive hot-corner man of all time.

Three-plus seasons into his major league career, the once meaty-thighed, duck-footed wannabe catcher is now something else entirely: a challenger to the likes of Harper, Mike Trout, and Manny Machado for the title of best all-around player in baseball.

When the Rockies drafted Arenado with the 59th overall pick in that 2009 draft, they did something many other teams wouldn't: They abandoned the idea of sticking him behind the plate. Colorado's brass did share the industry view that he was too big to play short. Instead, the team's scouts saw that great arm and pegged him as a third baseman. If Arenado could shed some baby fat and improve his agility, they thought, he might become pretty decent at the job in time.

As his minor league career began, Arenado showed off his hit tool immediately. Not a huge slugger by any means, he succeeded instead by putting balls in play, and with good situational hitting. He batted .300, .308, and .298 in his first three minor league seasons, driving in an eye-popping 122 runs in 134 games in 2011, at High-A Modesto. Though a hitter's ability to drive in runs depends in large part on having runners on in front of him (playing in the hitter-friendly California League doesn't hurt either), Arenado's contact skills still stood out with runners on base. He fanned in just 10.3 percent of his minor league plate appearances.

Arenado is reaping the benefits of hard work and attention to detail this season in Colorado. USATSI

"He was able to get runs home, and he did that a lot of different ways," said Jeff Bridich, the current Rockies GM who formerly served as the team's director of baseball operations, and then as senior director of player development. "Some of it was with home runs, a lot of it was doubles. Sometimes it was just shooting a ball [to right field] because he was getting fed outside fastballs."

Arenado cites that 2011 season in Modesto as a jumping-off point for his career, especially on defense. Having already improved at third with help from then-minor league fielding coordinator Scott Fletcher, Arenado arrived in the Cal League to find additional help from then-Modesto manager Jerry Weinstein. Some of that was improving Arenado's routine, an important step given that this was just his third year playing third, just his second in a full-season league. Weinstein helped refine Arenado's starting mechanism, so he could get a better jump on balls. He also urged him to drop his old approach of crossing over his feet while preparing to throw, switching to a more traditional drop-step maneuver instead.

But perhaps the biggest factor was just reps. Arenado needed to get used to playing third. And while Weinstein and others praised his work ethic, Arenado said he appreciated getting a friendly nudge.

"Jerry really helped me because he was the one who always kept up with me," said Arenado. "He always pushed me. When I didn't want to take ground balls, he made me take ground balls. He made me get better. I used to get mad at him for it, but now I've learned to appreciate it, because now I feel I'm better because of him.

"I'm not a guy that goes out there and is like, 'oh I'm just good like this.' I know I have to work hard. I'm not arrogant about my defense. I know how hard it is to get to where I'm at, and I know I have to keep up with it."

Weinstein described Arenado as a creature of routine, someone who won't ever stop at 14 groundballs in a given drill, because he has to stick to his usual 15. Meanwhile, even as he worked to get in better shape, you could see his defensive instincts emerging. He'd know where to throw the ball without even looking, spearing a hot shot to third, then making a 360 spin-and-throw to first right on the money. By the fall of 2011, the industry was starting to take notice.

"Other managers in the [California League] would come up to me and say, 'Wow, he's really special,'" recalled Weinstein, now a Rockies special assistant for the scouting and player development departments. "I was sitting with Mike Scioscia at instructional league after that season, Nolan was playing in the fall league. Mike looks at me and says, "Hey, tell me all about that third baseman you've got!'"

The hard work at third paid off, as did Arenado's efforts to get in better shape. Beyond the usual road work and weight-room sessions that define every player's routine, Arenado said he's hyper-vigilant about getting proper rest and drinking massive quantities of water, to overcome the added grind that comes with playing at altitude.

"His body has changed so much," said one major league talent evaluator who watched Arenado in high school. "There is absolutely no way in hell you would have guessed he would become a defensive God."

Arenado made his major league debut on April 28, 2013. Since then, he's saved an astonishing 71 runs more than the average third baseman (per Baseball Info Solutions' Defensive Runs Saved). That total leads the majors over that span, topping Manny Machado, Evan Longoria, and every other defensive standout at the position.

Beyond mere numbers, every Rockies game offers a chance to see something special. Arenado's improved agility leads to gorgeous diving stops, and his terrific arm enables him to make all kinds of very tough throws. Then there are the truly spectacular plays, the ones that get shown on highlight shows all season long.

Had Arenado's progression as a player stopped there, that would have been enough to get him to an All-Star team or two. But the combination of better fitness, an obsession with routine, and the usual physical maturation that athletes see as they grow out of their teens also gave his hitting a chance to improve. Though Arenado showed promising pop in the minors, it was mostly doubles power: In 437 minor league games, he hit a modest 49 homers ... but also 137 doubles.

Coors Field's long ball-friendly elevation figured to add to his homer total a bit, but Arenado still wasn't quite seen as an elite power threat when he cracked the big leagues. He struck out a hair more than 13 percent of the time over those first two seasons, further underscoring the notion that he'd be an excellent contact hitter with good gap power in the Show, if not necessarily an all-world slugger. His first two major league seasons backed up that scouting report: In his first 244 major league games, Arenado cracked a respectable 28 homers, but also 63 doubles. Throw in one of the lowest walk rates in the league (Arenado drew just 48 free passes in 981 plate appearances over those first two years) plus a park adjustment for playing his home games at Coors, and Arenado rated as a better-than-average but far from elite hitter by the end of his 2014 campaign.

In 2015, everything changed. After missing 51 games due to a broken finger and a case of pneumonia in 2014, Arenado enjoyed his first full, healthy season, playing 157 games. And while he kept up his annual gaudy doubles total by lashing 43 two-baggers, something else happened too: He went long ball-crazy, leading the National League by smashing 42 home runs. Always an aggressive hitter, Arenado again walked in just 5 percent of his plate appearances in 2015, and actually struck out more than ever before, with a 16.5 percent K rate. But beyond those surface numbers, Arenado said 2015 was the year he finally started to truly figure out major league pitching.

"I struck out more, but I also started having more quality at-bats," he said. "I'd get myself in better hitter's counts." At 3.49 pitches per plate appearances, Arenado still rated as below average last season in terms of working deep counts. But he said he learned to curb his habit up of stepping to the plate and swinging at the first pitch on a whim. "I'm really taking everything in, I'm really focused on my pitch. I started really looking for the pitch I know I can drive, the one I can do damage on."

As tough as it is to improve on a season in which a player leads the league in homers and RBI, Arenado has done so this year. And this time, the results have been plainly evident in his underlying plate discipline numbers. He's swinging at fewer pitches out of the zone than ever before, making more contact on pitches both in and out of the zone, and thus swinging and missing less frequently than ever before. He's nearly doubled his walk rate, while also slashing his already moderate strikeout rate, amassing an equal 15 bases on balls and 15 punchouts in 150 plate appearances.

For Arenado, that change comes down to knowing his strengths, and also his limitations. Leading the league again this year with 13 homers (and batting a phenomenal .321/.393/679 overall), Arenado's now up to 83 round-trippers in his young career. Exactly zero of those have gone to the opposite field. So he's spitting on outside pitches he can't handle, and pulling pitches he can handle with authority, even on two-strike counts. Combine that approach with a career best in flyball rate (53.4 percent, highest in the National League), and you get a whole lot of this:

"You're just seeing continued growth," said Rockies manager Walt Weiss. "He's an extremely talented player who's continuing to mature. He's not even in his prime yet, as far as baseball prime goes. It's pretty exciting to think about that."

Exciting if you're a Rockies fan. Terrifying if you root for the other side.