CORPUS CHRISTI, Texas — At the end of spring training, it felt like J.B. Bukauskas was on the verge of pitching for the Astros.



As much as if not even more than fellow prospects Forrest Whitley and Corbin Martin, Bukauskas impressed just about everyone in his first big-league camp. The 2017 first-rounder was given a start at Minute Maid Park in the second of the team’s two late-March exhibition games against the Pirates, a reward before he was shipped back to Double-A Corpus Christi to begin the minor-league season.



But as soon as the season began, Bukauskas’s performance flipped from dominant to dreadful. In his first start, he surrendered eight earned runs in only 2 2/3 innings. His second outing, an extended relief appearance, saw him allow three earned runs in three innings. In his third start, it was six runs in 2 1/3. Before he knew it, he had a 19.13 ERA.



The extent of his struggles served as a reminder that the 22-year-old has work...