By Bruce Levine–

CHICAGO (CBS) — When Cubs manager Joe Maddon first saw rookie infielder/outfielder Ian Happ play in Mesa, Ariz., earlier this spring, he didn’t consider Happ ready yet for the big leagues or to be a regular for the defending champions.

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So much has changed since then.

The Cubs have been plagued by below-average performances from many players in a disappointing first half of the season. Happ has been an exception, which is why he’s become a regular, hit clean-up again for the Cubs on Saturday night and opened up the eyes of his own manager.

“I really didn’t know he was this good of an athlete,” Maddon said. “When I saw him for the first time in spring training, I thought I was just looking at a hitter. I was not convinced about his second base play. He has proven me wrong. The part that was not exposed was his outfield play. Now he has proven he can play out there too.”

Chicago’s first-round pick in 2015, Happ has progressed as quickly as Kris Bryant and Kyle Schwarber did through the system. Happ has been one of Maddon’s most productive sluggers while others have been out with injury or slumped. He’s hitting .264 with 13 homers, 30 RBIs and an .893 OPS in 50 games this season.

The 22-year-old Happ is an infielder by trade but has resided most often in the outfield this season. He has 32 starts in the outfielder and 12 at second base.

Happ’s work in the outfield is a process. An over-aggressive play in center field on Friday had Happ bumping into Schwarber in left center. The ball came out of his grasp, and he was charged with an error.

“We love his aggressiveness,” said Cubs bench coach Davey Martinez, who oversees the outfielders. “With more time out there, he will make fewer mistakes like that. He is extremely coachable. I believe he will be a better-than-average major league outfielder.”

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Happ is a quiet, well-thought out individual. His teammates point to a zone that he gets into during his at-bats.

“”I have felt comfortable here since day one,” said Happ, who made his big league debut on May 13. “The guys on this team made it easy by making me feel like I belonged from the beginning.”

Happ hasn’t been fazed by batting clean-up for the defending champion Cubs.

“I am enjoying every minute of this,” Happ said. “If that means hitting in the middle of the lineup, fantastic. I am really happy to be in an environment where you feel so accepted.”

Happ will be in the race for the National League Rookie of the Year award. Dodgers first baseman/outfielder Cody Bellinger is the front-runner for that honor right now, with 25 homers.

Happ pointed to the faith put in him by Cubs management for helping him stay afloat in the big leagues.

“There was a time a few weeks ago when I was really struggling,” Happ said. “They let me grind through it. I continued to make the adjustment. That was big for me.”

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Bruce Levine covers the Cubs and White Sox for 670 The Score and Follow him on Twitter @MLBBruceLevine.