When it comes to prospect returns in a trade, you have three basic categories.
You have the centerpiece. A player that's highly rated and is considered the most desired prospect in the trade due to strong likelihood of being a major league contributor. This player is usually in the mid-minors. Sometimes in AAA. Rarely in short-season or even low-A. Most likely in High-A or AA.
Then there's the short-term contributor. A guy that's probably in AA or AAA, possibly even the majors. He's a high floor guy. He won't be a star, likely a replacement level player at best.
Then the lottery ticket. The guy in the low minors and has a high ceiling but is raw in almost every way. Something about him physically is off the charts but there's plenty to speculate on. In the Cosart to the Marlins trade, this guy is Francis Martes.
Lets review some of his accolades. Baseball America had him as the 19th best prospect coming out of the GCL last year and the 15th best prospect in the Astros system. Not too bad. Being 19th in the GCL is an honor but top prospect lists from that league are littered in raw athletes that bust.
Martes has a chance to not be a bust as he has a shot at being considered for a full-season top prospect list for a league this year.
In eight games, his ERA is almost nonexistent at 0.88. There's a very low BABIP that's supporting that but his FIP is still solid at 3.24. He had a high walk-rate while with the GCL Marlins but it lowered after the trade. So far it's 7.1% which is right in line with his DSL stint and the GCL Astros numbers. The strikeout rate has dipped below 20% which is a concern since he's about 2% below league average. But, his KS% is about a percent above league average which correlates to his plus fastball reports.
Given the quality and distance of the video, there's not a whole lot you can take away from his mechanics. They don't look bad which always good. Just can't say he has great mechanics.
What to take away from is how quickly the fastball gets on hitters. That's true plus velocity as hitters are uncomfortable dealing with it and in this video have difficulty making contact against it. In fact, most of his whiffs in this video were on the fastball. He has some real nice spin up in the zone and flashes good movement down in the zone.
Something to notice is that the curve ball is not a big breaking curve. It has 11-7 break and flashes sharp break. But it can get away from him and is a work in progress.
The fastball will definitely play but he is your prototypical big armed fastball guy with lagging secondary offerings based on this video.