In the middle of April, I observed the Seattle Mariners' top prospect, Justus Sheffield. Advertised as a potential frontline starter, I came away mostly unimpressed. His fastball lacked zip. His slider was inconsistent. His changeup was almost nonexistent, and even the simple task of throwing strikes was a labored effort.
Since then, things have gotten even worse for Sheffield. In 13 games (12 starts) for the Tacoma Rainiers, he's posted a 6.87 ERA. He's had just 48 strikeouts (and 41 walks) in 55 innings and has allowed 12 balls to leave the yard. His most recent stretch of games was particularly terrible. Over his last four starts with the Rainiers, Sheffield allowed 23 runs in just 11 innings, walking nearly as many men (12) as he struck out (14) and serving up half of his home run total for the season.
One would think there is something physically wrong with Sheffield. However, he maintains that his arm feels good and his stuff is just fine. Furthermore, considering the stock the Mariners have invested in him, the organization isn't going to allow him to pitch if it knows about a physical issue.