It's been a work in progress for the immensely talented 20-year-old since his May 7 call-up, but Castro has settled down in the field and has hit well, too.
After Sunday night's game, an 11-6 win over the Phillies, Castro was 18-for-49 in July.
"You know what? He's a nice young player," said manager Lou Piniella. "He's been learning on the job up here. (Coaches Ivan) DeJesus and (Alan) Trammell have done a nice job with him. To the kid's credit, he's shown some doggedness. He's doing a really nice job for a young player. I've got no complaints whatsoever."
For that reason, Piniella made a lineup switch for Sunday's game, moving rookie right fielder Tyler Colvin into the leadoff spot and moving Castro up to second. Castro has batted seventh or eighth most of the year, with second baseman Ryan Theriot hitting first or second.
Castro extended his hitting streak to six games Sunday. He is 12-for-22 (.545) during the streak. He has raised his batting average to .294 and could become a fixture near the top of the order after batting seventh or eighth most of the time since coming up from the minor leagues on May 7.
"Truthfully, Castro's been swinging the bat a little better," Piniella said. "Moving him up to the two-spot, and we just move Theriot to the bottom. It's no big deal one way or another. The young kid's been swinging the bat well."
--RHP Carlos Zambrano is scheduled to throw at least an inning of a simulated game Monday in Arizona. He will join Class AAA Iowa and begin pitching out of the bullpen as early as Wednesday. The Cubs will wait for the road trip that begins July 26 at Houston to activate Zambrano, who has undergone treatment for anger-management issues.
--RHP Brian Schlitter has begun a rehab assignment at Iowa. Schlitter went on the DL July 5 with a right-shoulder impingement.
--RHP Carlos Marmol walked five (one intentionally) in one-third of an inning in Saturday's 4-1 loss to the Phillies. He became the first Cubs reliever since Johnny Vander Meer in 1950 to walk at least five in one inning or less. Marmol said he had no feel for his slider.
--CF Marlon Byrd was hit twice by pitches, giving him 16 for the season. It's the first time since Frank Chance in 1905 that the Cubs have had a batter hit at least 16 times.
"Yep, I don't get out of the way," Byrd said. "They try to throw the ball in. Sometimes they get it on the plate. Sometimes they don't. Sometimes I get on first. Sometimes I don't. It's just one of those things. Sometimes you're a magnet."