Ketel Marte’s one big adjustment

Heading into this offseason, the Mariners had two players who projected to be above average shortstops. Brad Miller had a couple of years of major league experience at the position; he had a little pop in his bat, could take a walk, but was known for lapses in throwing accuracy. Ketel Marte had just two months of major league experience; he had a more contact oriented approach at the plate, saw a huge jump in plate discipline in the bigs, and was pretty decent in the field. So when Jerry Dipoto traded away Brad Miller as one of his first moves of the offseason, it showed a lot of faith in Marte's abilities.

Dipoto hasn’t shied away from creating competition through depth on the roster, particularly at positions without a long-standing incumbent. After Marte on the depth chart stand Chris Taylor and Luis Sardinas, neither of whom profile as starting shortstops. Despite his limited time in the majors, Marte will be heading into 2016 as the unquestioned starter at one of the most critical positions on the field.

Marte spent roughly two months in the majors in 2015 and accumulated 247 plate appearances in that time. If you look closely, those two months look pretty different for him at the plate. By the end of the year, he was hitting for more power than he had ever shown in the minors. Observe:

Month	PA	BB%	K%	ISO	wOBA
July/Aug	115	9.6%	16.5%	0.089	0.312
Sept/Oct	132	9.8%	18.2%	0.144	0.346

During his first month in the majors, his slugging percentage was just a few points higher than his on-base percentage. In September, something clicked and his ISO jumped 55 points. To be fair, the sample sizes we’re working with aren’t ideal, but strikeout rate, walk rate, and ISO have very quick stabilization points. One hundred thirty-two plate appearances might not seem like much, but it's pretty close to being statistically significant.

The fact that he was hitting for more power than ever tells me he made some pretty sizable adjustments against the highest competition level. To try and figure out what happened, I went straight to the video (this was really an excuse to watch a ton of highlights). I’ll show two examples of his swing, one from August and one from September:

August 9:

September 30:

Both of these are offspeed pitches which is why he’s out in front of both pitches. But the differences are striking. In August, he’s flat footed as his weight is transferring. In September, his stride is more pronounced and it’s in rhythm with his hand load. He’s also standing more upright and he’s showing better hip rotation. I’ll show you one more example of his swing:

September 28:

That swing came in a 3-1 count and that ball traveled 371 feet. You can see shades of Robinson Cano in that swing. I just can’t imagine his swing in August generating enough power to hit a ball that far.

Besides just being mechanically different, some his plate discipline and batted ball peripherals changed in September too. You might have noticed a slight increase in strikeout rate in the table above. Part of that may be due to his whiff rate increasing by three points and his contact rate falling from well above average to just below league average.

Month	PA	Contact	O-Contact	Z-Contact	SwStr
July/Aug	115	85.6%	72.6%	92.4%	6.0%
Sept/Oct	132	78.8%	66.7%	85.1%	9.3%

In other words, he was making contact like Billy Burns in August and like Evan Longoria in September. That's not necessarily a bad thing, however. It seems like Marte was focused on making contact at the expense of all power when he was first called up. Narratively, this makes sense too. Making the jump to the majors is a pretty big step, so an approach focused on maximizing his strengths—his speed and his ability to put the bat to the ball—helped him gain confidence and built a foundation of success. As he grew more comfortable, and received instruction from coaching staff and other players, his swing opened up a bit more and he started hitting for some power.

His batted ball profile also shifted as the season wore on.

Month	PA	BIP	LD%	GB%	FB%
July/Aug	115	82	22.0%	57.3%	20.7%
Sept/Oct	132	90	21.1%	47.8%	31.1%

His line drive rate was stable across both months but he started hitting more fly balls in September. This also makes sense in context. Again, he began his major league career with a batted ball profile that maximized his strengths, but as he made adjustments, he began lifting the ball and driving it with power more often. It's no coincidence the two homers he hit in the majors came late in September after he made these mechanical adjustments.

Despite what we might have assumed, Marte does have a little power in his bat. An ISO of .140 might be his peak at this point, but I think he also showed that his bat isn’t completely devoid of pop. He's just 22-years-old and entering his physical prime. The true key to his success will be his ability to maintain his improved walk rate. But a little more power out of him certainly wouldn’t hurt either. The onus is on him to continue to work on these adjustments he made towards the end of the season. A shortstop with some gap power and the patience to take a walk is a very valuable thing. Maybe there didn’t need to be a competition at shortstop after all.