The rookie made three errors in his first game at Wrigley Field, one of which led to a run, in the Florida Marlins' 4-2 victory over the Cubs.
Castro is not the first Cubs shortstop to make three errors in a game. Shawon Dunston did so on April 15, 1985, which was his sixth game in his first professional season. Longtime Cubs shortstop Don Kessinger made three errors on May 30, 1966, in a game in Pittsburgh. That was his second full season.
The last Cubs player to commit three miscues in a game was Aramis Ramirez on Sept. 2, 2008. The Cubs now have at least one error in the last five games, the most since a six-game span April 4-10, 2009.
The mistakes are part of the learning process for Castro, the youngest player in the Major Leagues. He not only made two bad throws but didn't hustle after a ball that he tried to backhand in the eighth. The baserunner, Hanley Ramirez, hustled to second on the play.
"He got frustrated with himself," Cubs first baseman Derrek Lee said of Castro's third error. "He had a couple tough plays. I don't think he was trying to not hustle. He pouted for a second. He's 20 years old, he's young and he'll get better."
Cubs manager Lou Piniella called Castro into his office after the game to talk to him about the play.
"You have to go get the ball," Piniella said. "If you don't catch it, you can't let it lay there."
"He felt bad about that situation," coach Ivan DeJesus said, translating for Castro. "He needs to be more alert."
What do you say to Castro after a nightmarish home debut?
"Keep your head up, man," Lee said. "We've all had games like that. In 24 hours, we'll be out there again. You have to forget about it and be ready to go."
Soriano will say something to Castro as well. He invited the youngster to stay with him until Soriano's family arrives in June. Sunday was Castro's first night in Chicago since he was called up from Double-A Tennessee on Friday.
"I want to talk to him when we get home," Soriano said. "It's part of the game. He's good. He plays very good defense. I think he's a little nervous, first game in big leagues in Chicago. I had the same thing my first game in New York. I understand. You can be a little nervous. That's a dream for every baseball player to be in the big leagues. Now, at his age, to be in the big leagues, 20 years old, I think he can be a little nervous."
Bernie Williams, Mariano Rivera and Derek Jeter took care of Soriano in New York. Then, Soriano was playing second base. He heard boos, too.
"The most important thing is I had people behind me," Soriano said. "That's what I want to do for him. ... He has to learn from this and he'll be OK."
Before the game, Castro said he felt good about his start, now four games old. And now?
"Errors happen in the game," he said.
"All those guys [on the Yankees] made me feel [like] 'You're a young guy on the team but you're a part of this team and we need you,'" Soriano said. "They made me feel like I'm part of the family. To play with those superstars made me feel a little shy. I think that's happened to him, too. He doesn't believe he's in the big leagues. He'll be fine. He'll play every day in the big leagues, and he'll be fine."
Castro is 4-for-14 so far, making a splash on Friday when he drove in six runs, a Major League record for a player in his debut.
"He knows how to play," Lee said. "He's a good athlete. It looks like he has good baseball instincts. He's young -- he's extremely young. It's going to take him awhile to grow into his body. All the tools are there."
Castro worked out with Ryan Theriot, who has shifted from shortstop to second, before the game. That's a routine the two will do as much as possible.
"I think the more he plays, the better he'll field," DeJesus said.
"He's a talented young man," Piniella said of Castro. "He's going to gain experience at the Major League level. I think it'll be fun for fans to watch him play. The young man can play baseball."
He's going to be tested by Chicago fans. They have high expectations, and they booed after the third error.
"They shouldn't expect that much out of him, they should just let the young man play," Piniella said. "Let him play, let him relax and let him settle in as a good Major League shortstop."
Castro was batting .376 at Tennessee. At 20 years, 44 days, he's not only the youngest in the big leagues now but the youngest player to play shortstop in Cubs history.
"I didn't expect it to be so soon," Castro said of his callup.
Soriano also helped Castro find a barber to get his hair trimmed prior to Monday's game. Castro has the tools. He's fast, can hit, can field, and hit for power.
"What he has the most is his confidence," DeJesus said. "His mindset is there and he just needs to go out there and play.
"He's going to be great. Playing here in Chicago, he'll get a good opportunity and show his talent."
Carrie Muskat is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.