Casey Tefertiller

Bolt used a rough introduction to Double-A as a springboard to retool his swing. It paid off in a 40-man roster spot.

From platooning to bullpening, Bob Melvin is a leader for all the situations presented in Oakland.

Six years into his pro career, Barrera’s bat began showing signs of life to complement his strong running, fielding and throwing tools.

A sixth-round pick out of high school this year, Butler gained confidence in the batter’s box and in the outfield at instructional league.

A former Clemson shortstop, White added second base, third base and center field to his portfolio at Double-A.

Plus makeup and stuff propelled Jesus Luzardo from high Class A to Triple-A in a breakout season.

The 2017 first-rounder had never seen velocity in high school like he has in pro ball, but he just keeps improving with experience.

The cannon-armed catcher has emerged as a dangerous hitter, helping him win the system’s Best Player in our midseason update.

Ramirez showcased plus hitting ability as he climbed to Double-A, but his future position and power potential are not yet in focus.

Merrell can fly and doesn’t hit for much power, so Oakland will develop the shortstop as a table-setter.

Jesus Luzardo comes to the aid of those affected by the mass shooting at Florida’s Douglas High, his alma matter.

Teenager Lazaro Armenteros worked all winter to improve his only weakness.

Moving to the bullpen at Triple-A put Raul Alcantara back on a track to the majors.

Athletics OF B.J. Boyd changed his swing and outlook in 2017.

The Athletics love shortstop Nick Allen’s defensive fluidity and potential leadoff bat.

Casey Tefertiller chooses postseason award winners for Athletics prospects.

The Athletics could not be more pleased with second-rounder Greg Deichmann.

The versatile Sheldon Neuse could be the quintessential Athletics prospect.

A more aggressive approach paid off for Matt Olson at Triple-A.