A few days ago, we talked about the Puzzle of Kansas City Royals first baseman Eric Hosmer. Teammate Mike Moustakas also presents an unusual case. Like Hosmer, the third baseman was a top draft pick who performed well in the minors but who has not fully lived up to expectations in the major leagues, at least during the regular season. He's knocked four homers in the post-season thus far, but in the long course of three and a half major league seasons he's hit just .236/.290/.379, averaging 16 homers per 162 games with a weak wRC+ of 82, an identical OPS+ of 82, and just 5.3 career WAR.
The post-season power is well-timed, but what can we expect from Moustakas as a regular player going forward? Can he live up to the expectations generated when he was tearing through the Texas and Pacific Coat Leagues for years ago?
Let's look at the historical parallels.
Through age 25, Moustakas Top Sim Score comps (retired players only) are Ken McMullen, Gary Gaetti, Don Money, Ed Kirkpatrick, Clete Boyer, Dalton Jones, Joe Foy, Andy Carey, and Tommy Agee.
Boyer was the closest comp offensively with an 81 OPS+ through age 25 compared to Moustakas' 82. He didn't really get his bat going consistently until his late 20s and still finished with an OPS+ of just 86, but he was a superior defensive player (even better than the solid Moustakas) and finished with 29.6 WAR.
McMullen's OPS+ was rather better than Moustakas at 97 to that point in his career, and like Boyer his glove kept him in the lineup even when his bat wasn't great. Gaetti (OPS+ 90 through age 25) and Money (OPS+88 through age 25) were similar stories, showing some power and defensive ability but below-average offense overall to that point of their careers. Both eventually solved their early issues and had successful careers as long-term regulars.
Kirkpatrick was a jack-of-all-trades type and a better hitter in context (98 OPS+) despite extremely similar slash lines. Agee, an outfielder with much more athleticism than Moustakas, had an offensive surge in his late 20s until falling apart at age 30 due to injuries.
On the negative side, Jones never got his bat going and was out of the majors at age 26, which doesn't seem likely to happen to Moustakas. Foy was out of the majors at age 28. Carey devolved into bench work in his late 20s.
I think the best comps here positionally and statistically are Boyer, McMullen, Gaetti and Money, third basemen with strong defensive ability, power, but erratic production in the early going. Despite troubles, all four went on to have successful careers and for similar reasons: their gloves kept them in the lineup long enough for them to smooth out their offensive issues. Money may be the best overall comp of all, with a similar bat and similar defensive value putting his age 25 ending WAR at 5.7 compared to Moustakas' 5.3. Money finished with a 32.0 career WAR.
These types of parallels are merely suggestive, of course. Moustakas is going to have to make a lot of progress offensively to end up with even a Gaetti or Money like career. The point however is that it is entirely plausible that this could happen, if history is any guide.