Spring Training Prospect Profile: Bulked-Up Jonathan Sierra Could Be Primed for Power Surge

When Yonathan Sierra Estiwal was signed as a 16-year-old international free agent in 2015, every physical comp of him was to a young Darryl Strawberry. Now 19 and entering his third professional season, Jonathan Sierra is no longer as wispy as straw. Or Straw. Rather, he is a chiseled 6-foot-3, maybe closer to 6-4, and somewhere around 230 pounds. In addition to that size and the potential for power, Sierra is also known as a gifted fielder with a strong left arm.

Here’s a snippet from MLB.com’s scouting report on the Dominican native back in 2015:

Overall, Estiwal has been praised for his ability to hit in games and hit the ball to all fields. He has also shown some power in games and the ability to drive the ball to the opposite field. Scouts describe Estiwal as an average runner and say his arm might be a tick above average.

Estiwal does well in games, and scouts like his makeup. He’s been simply described as “a good baseball player who knows the game,” on numerous occasions.

To date, Sierra has gotten 405 at-bat in his two seasons. After putting up a .264 average with a stellar .384 on base percentage in the DSL in 2016, he struggled a bit in Mesa. His batting average shrank only a few points to .259, but his OBP plummeted to .332.

In watching a video of Sierra, it’s quite clear he is susceptible to breaking stuff and there’s a hole in his swing that he needs to learn to cover up.

These things can be fixed and they can be fixed quickly. The question is, will it happen this year?

Basic Info

6-4, 230 lbs.
Bats/throws: L/L
Signed as IFA 2015
Santo Domingo, Dominican Republic

Leveling Up

I’m not sure what to expect just yet from Sierra in 2018. I’d like to see him strike out less and hit more home runs, but that’s true of every prospect ever. His 25 percent strikeout rate in the DSL jumped to 33 percent in Mesa, though you sort of expect that from a teenager. He’s got all the potential in the world and just turned 19, so has plenty of time to mature as a hitter.

One of the great things that I’ve seen the Cubs do in recent years is to train their young hitters to be more selective. That’s what needs to happen with Sierra. The home runs will eventually come, of that I have no doubt.

Of all the places in the Cubs system for Sierra to play in 2018, Eugene is kind of built for him. It’s hard to get a ball out to left and left center, almost impossible to dead center, but he could pull one down the right field line over a short fence.

While it would be unreasonable to expect drastic improvement and huge power numbers this year, improvement and development are going to be essential. His walk rate needs to go up and the strikeout rate needs to come down. If those things happen, everything else should fall into place.

Sierra should get an additional 230-250 at-bats this year Eugene. Next year at South Bend should see a big jump, as he will likely log over 400 at-bats in close to 140 games.

It’s not hard to see Sierra coming into his own this season, though a true breakout might be a year away yet. If and when he does put it all together, he could be special.