The other three were once at the other end of the battery nightly as catchers, while Castillo's move is more unusual. Until a few weeks ago, he had been a once-promising shortstop prospect. Now, he is a member of the bullpen of the New York-Penn League's Batavia Muckdogs and in the midst of a very steep learning curve.
He steadily rose through the lower levels of the St. Louis Cardinals farm system, primarily playing in the Gulf Coast League in 2008, Appalachian League in 2009 and New York-Penn League last summer.
Said to be one of the best defenders in the system at his position and possessing a strong arm, Castillo seemed to hit enough, batting right around .260 in each of the last two seasons. He was named a 2010 New York-Penn League All-Star as a member of the Batavia Muckdogs.
Now 22, Castillo started the 2011 season with Class A Quad Cities. Over his first 31 Midwest League games, 103 at-bats, the right-handed hitter could not get untracked. His line was .194/.263/.252. He was returned to extended spring training where he remained until starting the short-season back in Batavia.
Playing behind a brighter prospect, Cesar Valera, Castillo could not recapture his earlier success at the plate as his career momentum stalled. The right-handed hitter slipped to a .176 average in his first 11 games with the Muckdogs this season. He played his final game at shortstop on July 21, when he went 0-for-3 with a strikeout.
Cardinals farm director John Vuch was among those who came to the conclusion that a change was needed.
"This was a big year for Yunier as a shortstop," he said. "It turned out that his 2010 was better than his 2011 both offensively and defensively, so we felt the time was right to make the switch."
He explains how it came about. It was not a snap decision.
"This was something that was initially brought up earlier in the year, but we wanted to give Yunier every opportunity as a middle infielder first," Vuch said. "When it became apparent that it would be unlikely for him to reach the major leagues as a shortstop, he was given the opportunity to throw for (minor league pitching coordinator) Dyar Miller and our Batavia staff."
The coaches liked what they saw.
"The reports were positive, as he showed an above average arm from the mound, so we informed him that we're now looking at him as a pitcher," the farm director explained.
Castillo remained with the club while he began his conversion. The plan was for him to throw some side sessions and then a couple of simulated games before being worked into live game action.
He was deemed ready to make the final step Monday night when Muckdogs manager Dann Bilardello called him out of the bullpen to pitch the sixth inning on the road against the Connecticut Tigers. It was not garbage time by any stretch of the imagination as Batavia was clinging to a 5-3 lead.
"Yunier is excited about the change, and we're hopeful that he can follow in the footsteps of some of our other successful conversion pitchers," Vuch concluded.
No matter where his travels take him, Castillo should always remember his official pitching debut with satisfaction. He logged a perfect inning on two groundouts and a strikeout, and earned a hold in the process.
Brian Walton can be reached via email at email@example.com. Also catch his Cardinals commentary daily at The Cardinal Nation blog. Look for his weekly minor league column on Thursdays at FOXSportsMidwest.com. Follow Brian on Twitter.
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