"Usually, you can tell by the sound off the bat," Headley said.
It happened Wednesday, in the seventh inning of an otherwise forgettable 13-5 loss to the Giants, when Headley ran into a 93-mph fastball from Giants reliever Sandy Rosario.
In an exasperating season where not nearly enough has gone right for Headley or the Padres, there was the sound again, one that essentially reverberated throughout Petco Park.
The result was a near-miss, a long fly ball to center field that chased Giants center fielder Juan Perez to the warning track.
"I just got under it a tick," Headley said.
To be sure, Headley -- one year removed from one of the most successful single-season performances in franchise history -- hasn't heard this blissful sound nearly enough in 2013, nor has he seen the results he or the team have expected.
It's been a precipitous fall, one that has befuddled Headley, who is still searching for answers each day, each at-bat, each swing.
"I think I am being pitched to a little differently. Guys are being a little more careful. But I think a big part of it is I've swung at pitches I typically wouldn't have swung at," Headley said. "When you do that, they don't have to get in. They can keep throwing their pitch every time. There's been a lot more offspeed pitches. I haven't done a good job adjusting to that."
Could Headley's luck be changing? He hit a long home run to right field earlier in the game, lined out to second base and then, of course, had the near-miss to center field on what might have been the ball he hit the hardest in the game.
"I felt like I took some good swings all day," Headley said.
The question Headley and the Padres have is this: where has that swing been all season? A year after he led the National League in RBIs (115) and hit a career-high 31 home runs, Headley will head into Friday's game against the Rockies hitting .240 with nine home runs and 37 RBIs in 441 at-bats.
"The swing just hasn't been where I'd hope it would be all year," Headley said. "There are probably a lot of little things that go into that. I haven't really been right for any extended period of time. There have been a few games here and there where I started to feel as if I was getting there and then would get away from it again."
So what exactly happened to Headley this season? Even he isn't quite sure, though he's certain that it's not one thing. Has he been pitched to differently? No question. Has he been susceptible to breaking balls? At times, absolutely.
So which is the true Chase Headley -- the 2012 model or this current incarnation?
"It's a tough question. I've been asked that a lot," said Padres manager Bud Black. "He had a spectacular year a year ago. It was a great year. But I think to ask a player to hit 31 home runs and knock in 115 runs is a bit unfair. I think this year is not indicative of the type of career Chase is going to have moving forward.
"Is it somewhere in-between? I don't know. But it's not this."
It's been a struggle from the start of the season. Well, actually before the season, as Headley missed the first 14 games of the regular season after fracturing the tip of his left thumb while sliding during a Spring Training game on March 17.
Headley hit .261 in April, .243 in May and then in June, his average for the month plummeted to .183 as he had more strikeouts (27) than hits (20). He hit over .260 in July and August and, as mentioned before, had productive at-bats in Wednesday's game, his first of September after missing five games with back spasms.
Now, he just wants to finish strong.
"I just want to get back to what I know I can do," Headley said. "I feel like I've made some strides the last couple of weeks with some feel things in my swing that are starting to feel right again. Obviously, this is not the season I had hoped it would be."
Headley's zone contact rate, according to PITCH/fx has dropped from 85.2 percent in 2012 to 83.3 percent this season. His walk rate is down, his strikeout rate up. And Headley's HR/FB ratio (home run to fly ball) has dipped dramatically, from 21.4 percent a year ago to 9.2 percent.
"I think the home run and RBI explosion got a lot of people's attention. Whether that will show up again, I don't know," said Padres general manager Josh Byrnes said. "… But his durable play, he's turned into a good third baseman, a switch-hitter who can matchup with a lot of pitching, he still gets on base, [so] that still makes him a very valuable player."
But how valuable remains to be seen, at least in terms of his financial worth. Headley is making $8.575 million this season and is under control through 2014. The Padres have stated they would like to keep him, with executive chairman Ron Fowler suggesting earlier this season that a long-term deal could be in the works. Headley, 29, reiterated that he didn't want to talk about a contract until after the season.
Headley still sees a future for himself in San Diego, the only organization he's known, the one that drafted him out of the University of Tennessee in the second round of the 2005 First-Year Player Draft.
"Obviously, my first choice is to stay in San Diego, long term," Headley said. "If the organization is interested in talking long term … and I'm here for another year anyway. I don't want to put words in anyone's mouth, but it would be a prudent discussion in the offseason to see where each side stands."
Until then, Headley will keep his focus on the final 23 games, regular opportunities to produce, to get better, to get back to finding that success -- and that sound -- he had a year ago.
"Of course you're frustrated and it gets to you," Headley said. "You think about it when you go home, you think about it in the cage, you think about it all the time. But you have to show up each day refreshed, thinking that today is going to be the day it turns for you."