© 2014 MLB Advanced Media, L.P. All rights reserved.

5/28/2014 3:52 P.M. ET

Cubs hope to improve Castillo's caught-stealing rate

SAN FRANCISCO -- Welington Castillo entered Wednesday ranked third among National League catchers in fielding percentage, but he's also tied for first in most stolen bases against, throwing out only five of 36 basestealers. There are other factors involved -- such as the timing of a pitcher's delivery -- but Cubs manager Rick Renteria said they're working with Castillo on improving his numbers.

"We've had some plays where runners should've been out and they weren't because we probably had a dropped ball or missed tag or something of that nature," Renteria said. "We have to take it all into consideration. Do I think he's throwing the ball well? Yes. Is he able to better his numbers over the long haul? Probably."

On Tuesday night, Renteria considered challenging a call at second base in the fifth when the Giants' Angel Pagan was ruled safe on a stolen base. Shortstop Starlin Castro didn't seem to get his glove down for the tag.

"It's instinctual for an infielder to try to tag the runner, to chase the runner," Renteria said. "We talk about straddling the bag and taking the tag to the ground, which gives you a better chance to get the foot or hand."

Renteria said they don't want the pitchers to change their delivery in an effort to stop potential basestealers.

"The reality is a lot of pitchers don't worry about the stolen base because they feel they can go ahead and get the hitter," Renteria said. "If I want to make it an issue, then I'm taking away from the pitcher's ability and focus and doing what he needs to do against the hitters. I don't want to do that."

Parker impressed by Cubs prospects Baez, Alcantara

SAN FRANCISCO -- Cubs reliever Blake Parker thought the longest home run he'd ever seen was hit by former teammate Brad Snyder off the right-hander in the Minor Leagues. That was until Cubs top prospect Javier Baez connected recently for Triple-A Iowa.

Parker, called up Tuesday when Wesley Wright was placed on paternity leave, has had a front-row seat to watch Baez, who was batting .225 at Iowa with seven home runs and 25 RBIs. Baez has been the focus of attention as Cubs fans keep wondering when the shortstop will be promoted to the big leagues.

"I think he's handling it real well," Parker said Wednesday. "Early in the season, I think he had high expectations for himself. He wanted to do a whole lot for the team; he always wants to produce for the team. He's staying within himself now and he's producing for us and doing what he's supposed to be doing."

Baez also has struck out 56 times in 151 at-bats at Iowa.

"He's a free swinger, obviously," Parker said. "He gets his hacks in -- that's his game. Swinging at good pitches is the key to him having success and hitting the ball for power."

So, how close is Baez to the big leagues?

"He's coming," Parker said.

Another player to keep an eye on is Iowa second baseman Arismendy Alcantara, who was batting .281 with five homers and 25 RBIs.

"He's one of those guys you see coming up to the plate, and you think, 'Here's a little slap lefty' and then he drops the head on you for a homer or a double," Parker said. "He's producing and getting hits when there are runners on base. He's doing the same thing -- seeing good pitches and working at-bats and playing the role he needs to play. He's playing a good second base. He's another guy to watch. He's another real impressive player."

Renteria pleased with revised replay system

SAN FRANCISCO -- So far, the new replay review system seems to be working, Cubs manager Rick Renteria said.

"I feel we've gotten more calls corrected that might not otherwise have been corrected," Renteria said Wednesday. "I still think [replay] alleviates the umpires from so much scrutiny. They want to get the call right. They're human beings, they make mistakes, but they're doing their best.

"You've got to give them credit -- it's not the easiest job in the world to be an umpire."

Renteria would know. He's been ejected three times this season and was the first manager to get tossed in the regular season.

"The guys who I have a difference of opinion with were pretty patient with me," he said. "I thought they were very professional. They give me 15, 20, 30 seconds to say what we need to say. At least in my case, they've allowed me time to say what I say."

Extra bases

• Wright, on paternity leave, welcomed daughter Harlem Rose on Tuesday in Chicago. Wright left San Francisco late Monday to be with his wife, Sherell, for the birth of their second child. Wright was expected to rejoin the Cubs on Friday in Milwaukee for the start of a three-game series. The lefty has held right-handed hitters to a .154 average, second-lowest mark in the Major Leagues.

• Reliever Pedro Strop, on the disabled list since May 7 with a left groin strain, was getting close to making a rehab outing, Renteria said Wednesday.

Outfielder Ryan Sweeney, sidelined since May 3 with a right hamstring strain, was running 75 to 80 percent and had no tightness or soreness. There was no timetable for his return.

Both Strop and Sweeney were rehabbing at the Cubs' complex in Mesa, Ariz.

• Parker, called up to take Wright's spot in the bullpen, landed in San Francisco around 6:30 p.m. PT, reached the ballpark by the fourth inning and was called on to pitch in the seventh.

"It's not the first time I've done that," Parker said. "You're always ready and expect to pitch every day when you get called up. It took me some extra stretching."

He faced four batters in the seventh and gave up a single.

Carrie Muskat is a reporter for MLB.com. She writes a blog, Muskat Ramblings, and you can follow her on Twitter @CarrieMuskat. This story was not subject to the approval of Major League Baseball or its clubs.