KANSAS CITY, Mo. — Rookie catcher Zack Collins was optioned to Class AAA Charlotte after the Sox’ 5-2 loss to the Royals on Monday. Catcher Welington Castillo (oblique) has completed his minor-league rehab at Class AAA Charlotte, was returned from his minor league rehab assignment and will join the team for its game against the Royals Tuesday night.

Collins, the No. 10 overall pick in the 2016 draft, was 2-for-26 with 14 strikeouts and five walks since his call-up from Charlotte.

“I definitely learned from my experience here,” Collins said. “I know what I have to do to come back and succeed. I’m going to go down and do it.’’

“I guarantee you he will walk away from this experience understanding the differences and the depth between Triple-A and the major leagues,” manager Rick Renteria said.

Collins’ defense behind the plate has been undistinguished at all pro levels, and the Sox are adding first base to his game in hopes of building versatility. He had taken ground balls with coach Joe McEwing daily and was all ears, Renteria said, in hitting and catching discussions with coaches.

“He knows he’s going to make some adjustments,” Renteria said. “He knows . . . in time we’ll continue to give him opportunities to do what he’s doing. He’s taking them in with an open mind, and he’s been very honest with himself and the coaching staff.”

Castillo appeared in five games with Class AA Birmingham and Charlotte on his rehab assignment, going 5-for-21 (.238) with one home run and five RBI. He is hitting .196 with five homers and 15 RBI over 34 games with the White Sox

McCann’s long-ball theory

The baseballs may very well be juiced in 2019, but Sox catcher James McCann isn’t ready to pin the record-setting home-run pace entirely on the balls.

“It’s a different game,” McCann said. “Ten, 15 years ago, 90 percent of pitchers were throwing sinkers. It’s harder to hit a homer on a ball that’s intended to be hit on the top half and on the ground. Now every pitcher is throwing four-seamers up in the zone. When a hitter catches a four-seamer in the top of the zone properly, it’s already backspinning, and it’s going to go a little better.’’

McCann also said pitchers are not as committed to command as they used to be.

“Nowadays, it’s about velocity,” he said. “More [pitchers] have the grip-it-and-rip-it mentality, and when that happens, there are mistakes, and when you make mistakes to big-league hitters, they take advantage. Whether the ball is juiced or not, it’s easier when a ball is elevated out over the plate to get extended than it is when a guy is throwing heavy two-seamers down in the zone.

“There very well may be something different about the ball, but I know for a fact guys are pitching different than they used to.”

This and that

First baseman/designated hitter AJ Reed struck out three times in three plate appearances and is 1-for-10 with five strikeouts since the Sox claimed him on waivers, rescuing him from the Astros’ minor-league system.

† Outfielder Jon Jay had four hits, including two doubles, raising his average to .353.

He’s the first Sox player with four hits in a game without an RBI or run since Alex Avila did it against the Red Sox on June 23, 2016.

† The Sox were 1-for-13 with runners in scoring position.

The team is hitting a measly .136 with runners in scoring position in its last eight games.