So that explains Brandon Moss' slump

Oakland A's slugger Brandon Moss made the All-Star team after a monster first half in which he hit .268/.349/.530 with 21 home runs in 89 games. In the second half, he's hit .179/.312/.280 with four home runs in 52 games.

He missed Wednesday's game and Susan Slusser of the San Francisco Chronicle reports that Moss has been playing through a hip injury that will require offseason surgery:

"It was worse that we thought it would be," said Moss, who had an MRI and a cortisone shot before the game. "The shot should help me get through the rest of the season, but it won't fix it."

Moss told The Chronicle that the previously unreported problem has affected him much of the year and the MRI showed so much torn cartilage that he has bone-on-bone issues. He didn’t want to blame his second-half numbers dip on the problem but Moss said that he does not have much range of motion or strength in the joint as a result.

I'll go out on a limb and suggest the hip has affected Moss' production more than the loss of Yoenis Cespedes "protecting" him in the lineup.

Moss' types of contact haven't changed all that much from the first half to the second half:

First half

Groundballs: 33 percent

Fly balls: 45 percent

Line drives: 22 percent

Second half

Groundballs: 31 percent

Fly balls: 48 percent

Line drives: 21 percent

The big change? His fly balls traveled an average distance of 283 feet in the first half but just 261 feet in the second. Moss didn't use the hip injury as an excuse but it certainly seems to help explain the second-half decline.

For more on Moss and his approach as a hitter, Eno Sarris of FanGraphs just had a great interview (with Adam Dunn joining in as sidekick). Their exchange about the value of batting average is priceless (note: some salty language involved) as is Moss talking about how, when he was in Triple-A with the Phillies, Ruben Amaro didn't believe in him. ("He was like 'We just don't believe Brandon Moss is consistently able to hit a major league fastball.' And I was like, that's really all I kinda hit. It's my best pitch. Everything else, I just hope I hit it.")

Moss' groundball rate did go up in August -- which he noticed, telling Eno:

And that's what I was doing a lot in August, I was swinging wildly, trying to do too much. And therefore, that's when the weak outs, and that's when the ground balls started coming, was in August. My ground-ball rate kinda skyrocketed. Strikeout rate went up, chase rate went up, walk rate went up because I was taking more pitches, but when I was swinging, I wasn’t swinging to drive the ball, I was swinging to get a hit. That’s why I said in late August, screw this, I’m going to cover this pitch, I’m going to gear for this pitch, and if I walk I walk, and if I strikeout I strikeout.

From the interview, you can see why Moss is an A's type of player: Analytical, fun, understanding of his strengths and weaknesses. He didn't talk about the hip injury but he's going to play through it as the A's inch closer to clinching a wild card (their magic number is two).