The Josh Donaldson story is pretty amazing. The 48th pick in the 2007 draft, he was then traded a year later as one of four players going to Oakland for Rich Harden, as the Cubs were partially convinced to let him go due to his poor .217/.276/.349 line in A-ball that year. You generally don’t like it when college draftees put up a 78 wRC+ at any level, much less one they should be dominating. The A’s took a bet on a guy with contact skills and some power, though, and saw him hit much better upon promotion to the Cal League, but the league environment is pretty friendly there, and his slow start in Chicago raised questions about how good his bat would eventually become.

As a bat-first catcher, that’s a problem, so Baseball America ranked him as the A’s 13th best prospect following the 2008 season. That general ranking stuck for the next few years — he ranked as the A’s #14 prospect after 2009, #12 prospect after 2010, and #20 prospect after 2011 — as he kept performing like a good-not-great hitter, and one who mostly caught but also got some time at the corner infield positions, signaling that his future probably wasn’t behind the plate.

The A’s officially converted him to third base full time in 2012, as projected starter Scott Sizemore tore his ACL in spring training, and the A’s needed a replacement. But he flopped in that audition, hitting .153/.160/.235 in 100 plate appearances before getting shipped back to the minor leagues, losing his job to Brandon Inge, who signed with the team as a free agent in April after being released by the Tigers. At that point, Donaldson was a 26 year old with a big league wRC+ of 8. Yes, 8. Given his pedestrian minor league numbers, it was easy to look at Donaldson just like every other guy tweener, with a bat good enough to hang around the highest level of the minor leagues, but without enough value to stick as a big leaguer.

A couple of months later, though, Inge headed to the disabled list, and Donaldson was summoned back to replace him. And since August 14th of 2012, Donaldson has hit .287/.372/.519, good for a 146 wRC+, while turning himself into one of the very best players in baseball. And he just keeps getting better.

During his breakout 2013 season, Donaldson showed excellent control of the strike zone and hit a bunch of doubles, making himself kind of a classic A’s player. In his monster season last year, where he won the AL MVP, he added high-level power to that mix, launching 41 home runs. This year, he’s taken the power up another notch while also cutting his strikeout rate back down to where it was when he was a doubles hitter.

This is not the kind of career arc you see every day.

Most hitters have to make a choice between hitting the ball hard and avoiding strikeouts. If you watch Giancarlo Stanton crush a baseball, it’s easy to see that he’s making a choice to swing as hard as possible, accepting that he’s going to miss a lot in order to get maximum value when he does make contact. Donaldson, though, is hitting the ball ever harder without sacrificing any of his contact skills; his current 77.1% Contact rate would be the second-best mark of his career, despite the fact that league average contact rates have continued to fall as pitchers throw ever harder.

Like with Daniel Murphy and Matt Carpenter, the continued improvement seems to correspond with an acceptance of the value of elevating the ball. Donaldson came into the league as a guy who hit the ball to all fields and hit roughly an average number of groundballs, but he’s been moving towards a pull approach ever since, and this year, he’s appeared to make a conscious decision to get under the ball more often.

Donaldson is not yet Jose Bautista or Edwin Encarnacion — both of whom pull the ball more than half the time they put one in play — but he’s moving in their direction, realizing that pulled fly balls are the key to racking up a ton of extra base hits. And that shift has allowed Donaldson to become an elite slugger; he currently ranks second in the AL in ISO, behind only David Ortiz. And by becoming a high-level slugger while maintaining his control of the strike zone, he’s begun to induce those fear-walks that he wasn’t getting earlier in his career.

Even in a terrorizing line-up, pitchers have stopped throwing Donaldson strikes, and he’s been disciplined enough to lay off pitches out of the zone, leading to better hitter’s counts and more opportunities to swing for the fences without risking a strikeout. The end result? Donaldson is putting himself in the conversation for best hitter in baseball. For instance, take a look at these numbers from the last calendar year.

Donaldson and Trout, Past 365 Days Player PA BB% K% ISO BA OBP SLG wOBA wRC+ Mike Trout 700 15% 20% 0.277 0.312 0.419 0.589 0.423 175 Josh Donaldson 723 14% 17% 0.302 0.298 0.401 0.600 0.419 166

Trout’s got the longer track record, so we can be more confident that he can keep this up, but for the last year, Donaldson has been nearly his equal. And when you’re nearly the equal of one of the best players of all-time, well, you’re doing pretty well.

And it’s not like Donaldson has turned into a bat-only player. As I noted a few weeks ago, he’s stolen 23 consecutive bases without being caught, and has turned himself into one of the better baserunners in baseball, supplementing his offensive value. And he remains a terrific defender at third base, so over the last year, he’s pushing up against +10 WAR.

Somehow, when aging curves seem to be getting more extreme, Donaldson is getting better as he gets older. Now 30, he’s having a better year than he did in his MVP season last year, and if he keeps finding ways to improve his game, he may very well add another trophy or two to his resume before his career ends. That’s not bad for a guy who looked like a 4A player less than five years ago.