The early returns from Mariners rookie Ketel Marte

It has been a rather disappointing year for the Seattle Mariners, a disappointing year that cost Jack Zduriencik his job as General Manager. One of the few bright spots has been the play of shortstop prospect Ketel Marte, promoted to the major leagues in late July. A reader recently asked for an updated take on Marte based on the early results. Marte is past the rookie playing time limit; he won't be eligible for prospect lists entering 2016, so let's take a look.

Marte was signed by the Mariners out of the Dominican Republic in 2010. He cost just $100,000 but emerged as an intriguing talent with a strong season in the 2013 Midwest League. By the end of 2014 he was in Triple-A, at age 20, and well up the Mariners prospect depth chart. Here is the report on Marte from the 2015 Baseball Prospect Book:

Good points for Ketel Marte: He makes easy contact. He’s fast and aggressive on the bases. He shows good range at shortstop. He started to show more pop to the gaps last year, and he’s been very young for his leagues, playing 2014 in Double-A at age 20. Bad points for Ketel Marte: He is a very aggressive hitter and seldom draws walks, making his OBP extremely dependent on his batting average. That’s one thing if you’re hitting .300, but not if you drop down to .260. Scouts aren’t sure he has the body frame to add the strength necessary to drive the ball deep more often than he already does. His arm is mediocre and he doesn’t always show the instincts and concentration needed to compensate, leading some observers to project him as a second baseman, where his bat would be less valuable. We had him as a Grade C+ last year and with a good season under his belt we have to move his rating up, but I advise a little caution with expectations. Age-relative-to-league is important, but it isn’t everything. Grade B-.

Marte hit .314/.359/.410 in 261 at-bats for Triple-A Tacoma before his promotion to the majors. With Seattle he's hitting .268/.341/.346 with 18 walks, 33 strikeouts in 153 at-bats.

Basically, Marte's performance in the majors is almost exactly what we should expect it to be given his minor league track record. He makes contact but lacks power, as expected. His batting eye is perhaps a little better than anticipated, which helps keep his OBP near .340 despite the .260ish average. That's a good thing. His defense has been solid according to traditional metrics (fielding percentage, range factor) at or slightly better than league average.

The more advanced metrics like his glove even more. Despite the so-so bat, the glove boosts his fWAR value to 1.1 in 175 plate appearances. If he played a full season and maintained the same offensive production and current defensive skill, his fWAR would be somewhere between 3.5 and 4.0, which would make him one of the best shortstops in baseball. Overall his defensive play has been strong and at the higher boundary of pre-season expectation.

Of course, we can't assume that Marte would continue to play like this over a full season. Fatigue could set in at some point; pitchers could make adjustments, a slump could come, etc.

Still, 2015 represents a very promising start to his career. If he merely maintains his current skill level over a longer haul, he will be a regular for years to come. If he eventually adds more power to the mix, he could be an All-Star.