"The problem with him is the routine play more than anything else," Maddon said. "I really believe you can get a Major League-caliber infielder to make the routine play. He's had a couple mistakes, I don't disagree, but for the most part, I've been fine with him at shortstop."
Fans aren't as accepting, and some in the crowd booed after Castro's second error, when he couldn't handle Denard Span's grounder in the ninth.
"The last play, I don't know if that was a product of his last at-bat or not," Maddon said of Castro, who had grounded out to end the eighth and strand two runners. "For the most part, he's done a pretty good job on the double play."
An error by rookie second baseman Addison Russell led to one Nationals run in the fourth.
"We have made a lot of really good plays on defense, and the one that seems to bite us is more the routine stuff," Maddon said. "That's just repetition and technique. It's just being fundamentally sound, and we're working on it always. I will never denigrate the work of this group or the coaching staff. [The mistakes are] a little bit of a youthful thing."