For those who might have missed this development, Mike Moustakas has been good this season. Really good. Really ridiculously good even.
The season is still young, but to date, it's borne witness to the young Moose batting .313 with a solid walk rate and a *.232 isolated slugging percentage*. True to his Royal roots, Moustakas already has 11 doubles over just 27 games played. Taken together, his offensive contributions produce a .398 wOBA, about 56% better than a league average hitter.
While Moose's bat so far has been a very pleasant surprise, we can expect his offensive numbers to regress a bit over the course of the season. Moose is making hard contact, and there's reason to believe that the power is real, but flyball hitters don't maintain a .351 BABIP indefinitely. What's really going to propel Moustakas to the top of the WAR charts all season will be his defenive improvement.
Coming through the minors, everyone believed Mike would hit, but the knock on him was his defense. He had a great arm, but scouts thought his "thick lower half" would limit his agility, and he'd remain a below-average defensive third baseman. But when Moustakas arrived in spring training this season, the "thickness" had disappeared, and we're seeing what happens when you combine a cannon arm with good agility and an indomitable will to improve. His defense to date has passed the eye test with flying colors, registering a number of highlight plays, and the defensive metrics largely agree with what our eyes tell us. In only 27 games, UZR has Moustakas's at 4 runs better than the average third baseman while DRS (aka Dewan's +/-) rates his defense as 2 runs above average.
Like Moose's BABIP, his UZR pace will likely taper off some, so he won't wind up at +30 runs saved by the end of the year, but I think it's fair to expect Moose to continue to be an above average third baseman to the tune of another 3 to 6 runs saved over his next 120 games.
So where will Moose stand among MLB position players if going forward, he maintains his power, posts a normal BABIP in the low .300's and adds another 4 runs saved on defense?
ZiPS did most the math for us--it thinks Moose's BABIP will be .306 the rest of the way with 2 more defensive runs saved, and it largely leaves his power on its current track. If Moose does what ZiPS thinks he'll do, he'll finish the season with 5.1 WAR, among the Top 20 most valuable position players in the Majors. I think he'll outperform that defensive projection by a couple runs, while walk slightly more (~6% BB rate instead of the project 5.5% rate), and I even think he might even knock a few more balls out of the park. ZiPS forecasts 16 more Moustakas HR's this season, but I think his 8.9% HR/FB ratio is due to come up a bit. With as many balls as he's hitting hard in the air (55.6% flyball rate, which is quite high and may regress slightly downward), I see 20 more HR's as a reasonable possibility.
If, like me, you think Moose might outperform his ZiPS projection by a couple defensive runs and a handful of extra walks and HR's, you can expect him to wind up around 6 WAR for the season, which could place him well into the Top 10 position players or even the Top 5. And that's my best guess for his true talent--if he continues to have good BABIP luck, he just might actually win the MVP award.