Number 46 ranked Yolfran Castillo
Castillo is the lowest ranked MLB.com prospect of the group at 46, but he also is the most raw. He is a 6'3 and 175 pound shorstop. MLB.com describes Castillo as having, "a wide-open stance with a slight uppercut swing and lots of quickness. Castillo has a real feel for hitting and understands the strike zone. His hit tool exceeds his power tool for now, but there is a belief he will add more pop once he adds more strength".
Castillo is low-ranked it appears because scouts do not really know what to do with someone his size at this point. In the next few years as his body matures and fills out and if he does add power then he could be one of the Texas Rangers' top prospects. An infielder that can hit for power and play strong defense like he does already is very valuable. It will be on him to add muscle to his frame, develop his ability at the plate, and develop a stronger arm as MLB.com rates it as "average in the future". His arm from the description right now would be below-average.
Castillo and Martha are both being signed as shortstops and they join a bevy of middle infield prospects already in the organization. Those names include Justin Foscue, Jonathan Ornelas, Echedry Vargas, and Sebastian Walcott. That is not even including the names on the major league roster like Corey Seager, Marcus Semien, Josh Smith, and Ezequiel Duran. Texas is loaded in the middle infield. That will help them in the future be able to make trades from a position of strength and not hurt the overall depth of the minor league system.