Minding his own business and playing third base, Headley saw teammate Chris Young miss badly with a fourth-inning pitch to Derrek Lee. The ball ran up and in on Lee, grazing his left forearm, sending him tumbling to the ground as he tried to evade the pitch.
Then things got a bit wild.
"Second game, I hadn't gotten a ground ball yet," Headley said. "I hadn't even gotten a hit yet. I hadn't done anything. I didn't really know what to do. I had never been a part of one of those, not even in the Minor Leagues.
"I ran in and hung out in the back. I stayed out of it as much as I could."
This makes Headley smile, maybe not so much the moment itself -- a benches-clearing melee that essentially ended before it started -- but what has transpired with his career since.
Has it really been that long since Headley first arrived in the big leagues?
Headley isn't sure where the time has gone, though he's certainly covered a lot of ground in his career, from winning a Gold Glove to leading the National League in RBIs in 2012, to being the subject of trade and contract extension rumors, to becoming a durable and, ultimately, very good big league third baseman.
"It has been amazing," Headley said recently. "When you look back, every season feels like it's 10 years long when you're going through it. Then all of a sudden, you're seven years in and it suddenly seems like a long, long time ago."
On Sunday, Headley took his customary place at third base for the Padres in the season opener against the Dodgers. By the end of the season, Headley should rank fourth in franchise history in games played, trailing, among others, Hall of Famers Tony Gywnn and Dave Winfield.
Headley is no longer the wide-eyed 23-year-old who arrived at Wrigley Field not knowing what was ahead of him. Today, Headley is on the cusp of turning 30, he's married with a son, Colt, and has another kid on the way. His faith and family -- wife Casey and a Westie named Memphis -- have kept him grounded.
Time hasn't so much changed Headley, though times have certainly changed.
Headley will be a free agent after the season. With what is expected to be a very lean free-agent market, he could command -- and likely receive -- a deal that far exceeds the $10.525 million he'll make in 2014, especially if his agency, Excel Sports, fronted by Casey Close, continues to make lucrative deals like the ones it made for Masahiro Tanaka and Clayton Kershaw.
"Of course you pay attention to that," Headley said.
So will this be Headley's last season with San Diego, the only organization that he has ever played for?
"It could be," Headley said. "I think toward the end of the season, that's when it will really start to sink in. [The season is] such a grind, it overtakes you. So I really haven't sat back and reflected if this is my last season here or not."
While Headley has only known the Padres, he thought he could become the future Red Sox third baseman in the days leading up to the 2005 Draft. He was certain that San Diego liked him, though Boston doggedly scouted him leading up to the Draft, too.
"If we were guessing, I would say that I thought I would have ended up with the Red Sox, since they had a ton of picks early in that Draft and we had a lot of contact with them," Headley said.
The Red Sox had five of the first 47 overall Draft picks that year and had chances to pick Headley early. But they instead pegged four others, including outfielder Jacoby Ellsbury and also pitcher Clay Buchholz, who were important cogs in the team's World Series run last fall.
"He was a guy we had a lot of debate about," said Padres general manager Josh Byrnes, who was the assistant general manager of the Red Sox in 2005. "I sort of went out of the way with Chase, and I sat down and talked with him, to get a feel for him. I was impressed."
When the 66th overall pick rolled around, San Diego, busy loading up on college players, jumped on Headley, who had a .530 on-base percentage his final season at Tennessee.
"Before then, we were having a hard time developing position players, and Chase was sort of the poster child for what we wanted," said then-general manager Kevin Towers.
"Chase had the great pitch recognition, a sweet spot for contact on his bat and he was a switch-hitter. We might have overdrafted him just a little … but then again, he possessed all of the skills we wanted."
Looking back, Headley can see why he was the right fit for the Padres, who had a president and CEO at the time, Sandy Alderson, who was considered a founding father in baseball's on-base revolution while with the A's.
"I think I fit into their philosophy to start with," Headley said. "So I never had to force myself into what those guys were trying to accomplish."
That discerning eye and blossoming power served Headley well as he raced through the farm system -- doing damage at nearly every turn, which allowed him to reach the big leagues briefly during the 2007 season.
When Headley returned for good during the 2008 season, he returned as an … outfielder?
The team had Kevin Kouzmanoff at third base and was looking for ways to get Headley into the lineup. The club tried the outfield, hitting balls to him at Petco Park that January. On the day that experiment took place, the glare of the sun shined in Headley's eyes, testing his ability and confidence alike.
"I hated it," Headley said with a laugh. "I didn't hate it at the time, because I knew it gave me a chance to be in the big leagues quicker, so I embraced it in that sense. On the other hand, that's half of your game, your defense. I always thought I could be a good defender at third base."
Headley appeared in 82 games in the outfield in 2008 and played in another 114 games -- all in left field -- the following season before ending up back where he wanted to be, at third base.
"I did the best that I possibly could," he said. "I was learning on the job and it wasn't going to be my best position. I was really happy when I got the chance to move back. When I did that, I felt it allowed me to be more of a complete player again."
Headley has played for one manager (Bud Black), three team presidents and three owners. He's also had six hitting coaches. Headley has pulled elements from those hitting coaches and has been shaped by his experiences, developing his own style, his own plan.
"I have gotten more aggressive early in the count as I've gotten older," Headley said. "I've learned how to hunt pitches more than I used to and understand that you're probably not going to get more than one good pitch to hit in an at-bat."
That's the offense. Headley takes pride in his defense and durability, and not just for fear the team might stick him in the outfield again. Only Miguel Cabrera of the Tigers has played in more games at third base than Headley since 2009.
"He's done a great job of understanding the responsibility of being an everyday player and what it's like to be counted on," Black said.
Headley is a Padre today, but next season, who knows? As he did a year ago, Headley won't enter any contract negotiation with the team during the season. He doesn't want it to be a distraction for him or for his teammates.
In 2012, before the non-waiver Trade Deadline, Headley was the topic of frequent trade rumors. He remembers the sick feeling that it gave him, having to answer the same question each and every day -- from reporters, but also from family and friends.
"It wasn't if you're getting traded, it's when and where." Headley said. "I did my best to try and block that. I think I've learned from it and am better for it now."
The Padres and Headley have talked contract before, and they each know where the other stands. The two sides presently differ in opinion on both contract length and average annual value.
"There's enough ground in between us to where it wasn't going to work right now," Headley said. "We understood what they were saying and they understood what we were saying. I think we just couldn't find that common ground. But everything has been cordial."
The focus now, Headley said, is on the field and improving on his performance from a year ago, when he was never quite right -- the result of a fractured thumb in Spring Training that he admits to coming back from too fast, and a nagging knee injury he played through.
"Realistically, am I going to hit 30 home runs and drive in 115 runs every year? Probably not," he said. "That's not to say I can't do it. I want to get to those numbers as close to it as I can. I think I'm anywhere from an 18 to 22 home runs, 85, 95 RBIs [and] runs on a consistent basis player."
The future holds so many unknowns for Headley. But there is one absolute that Headley can be certain of, one that he's never been surer about.
"I believe there's a better player in there that I can bring out," he said. "There's never a satisfied state as a player. You're always trying to reach for more. I know there's more in me on a consistent year-to-year basis. That's what I'm trying to get to."