Matt Kemp says shoulder is fine as he continues to work on swing

A frustrated Matt Kemp was out early Friday to take extra batting practice. Apparently, he did not believe he had solved the mystery of his swing.

At the end of the batting practice he did his best Bo Jackson impression, breaking his bat over his thigh. Then he walked to the dugout and threw the two pieces into a plastic trash can with vengeance.

Later at his clubhouse cubicle, he was composed but unwilling to discuss his frustration with batting practice.

“I was just working on some things,” Kemp said. “I’m good.”

Not real good on the season, though. He has only two home runs and a .356 slugging percentage in his first 45 games of the season. He’s struck out 50 times in 174 at-bats.

And during the last homestand, Kemp told The Times’ T.J. Simers he could not fully extend his swing and was uncertain if it was physical or mental.

Kemp had major off-season shoulder surgery, but has otherwise continually maintained that his shoulder was fine. Friday, too, he said he was satisfied the shoulder was sound.

“Yeah, I am,” he said. “It’s not my shoulder.”

Manager Don Mattingly said there have been no medical reports that Kemp has been having any issue with his shoulder, but he has observed a slight difference in his swing.

“I noticed his swing getting cut off, but nobody’s said anything medically that his shoulder is tight,” Mattingly said. “When his swing is good, it’s center field, right-center. He still top-spins the ball to left field and always has.

“To me the key is, is he top-spinning into left-center or is he top-spinning the ball to short? That’s two different things. If he’s top-spinning in left-center and left field, it tells me he’s getting extension to a certain point and he’s cutting off just a little bit, but not that much.”

Mattingly, who took in Friday’s early batting practice for Hanley Ramirez, Dee Gordon and Kemp, said his center-fielder was simply trying to work through some swing issues.

“He’s not where he wants to be,” Mattingly said. “He’s frustrated out there. The biggest thing we want to do with Matt is try to keep the bat in the strike zone longer. Just from my standpoint of watching Matt the year before and this year, when he’s going good he’s driving the ball to center field, right-center.”

Last season in April alone, Kemp was hitting .417 with 12 home runs and a .719 slugging percentage.

Team President Stan Kasten said if Kemp’s problem was simply one issue, they would have corrected it by now. Meanwhile, the Kemp vigil continues.

“We won’t be as good as we can be until Matt Kemp returns to being the real Matt Kemp,” Kasten said.