It began at Heyward's introductory press conference on Dec. 15, when Chicago's new star outfielder fired a few candid, pointed barbs at his old club, the Cardinals. Emphasis on the "old."
"As everyone may have seen from the numbers that came out, I didn't take the highest offer," Heyward said, per CSNChicago.com's Tony Andracki. "But for me, a winning attitude and culture and the fact that this was such a young group that I could grow myself with and be 26 years old."
Andracki noted that Heyward accepted $184 million over eight years from the Cubs and reportedly spurned an offer "close to $200 million" from St. Louis.
"I felt like if I were to look up in three years and see it's a completely different team, that would be kind of be different for me," Heyward said of his decision to ditch the Cards, per Andracki.
And he got even more specific, listing catcher Yadier Molina, outfielder Matt Holliday and right-hander Adam Wainwright as Cardinals who are on the downslope.
We'll parse the validity of Heyward's assessment in a moment. First, the rebuttal, courtesy of the St. Louis skipper.
"I don't think we have anything to apologize for in having a group like a Holliday, a Molina, a Wainwright," Matheny said, according to Rick Hummel of the St. Louis Post-Dispatch. "Those are the kinds of guys everybody wants on a club."
“I don't blame him," Matheny added. "But I don't like it."
As trash-talking exchanges go, that's pretty civil. Heyward went out of his way to express admiration for the Cardinals organization at his presser, and Matheny likewise said he's "got a lot of respect for Jason as a person."
But make no mistake: This will be bulletin-board fodder for the Cardinals as they defend their division title against the upstart, hard-charging Cubbies (not to mention the Pittsburgh Pirates).
This rivalry didn't need momentum. The Cards claimed the NL Central with the best record in baseball last season before the Cubs bounced them in the National League Division Series.
If the first-ever postseason clash between these historic foes wasn't enough to get the regional juices flowing, nothing will be.
Now, though, Heyward has spelled out the terms. The Cardinals are the aging champs with creaky knees and a faltering right hook. The Cubs, meanwhile, are the spry challengers gunning for the knockout.
Is that a fair summation?
Undeniably, the players Heyward cited—Molina, Holliday and Wainwright—will be central to the Cardinals' success next season. Molina is 33 and had a second surgery on his right thumb after the first one, in October, "didn't take," per CBSSports.com's David Brown.
Holliday turns 36 in January and played only 73 games last year. And the 34-year-old Wainwright missed nearly all of 2015 with a busted Achilles tendon.
The Cubs' core, by contrast, is composed of MLB newborns. Yes, the roster features veterans—including left-hander Jon Lester and righty John Lackey, another free agent who jumped ship from St. Louis to Chicago this winter.
But four rookies—Kris Bryant, Addison Russell, Jorge Soler and Kyle Schwarber—were key contributors to last year's run. And others, such as 26-year-old slugger Anthony Rizzo and 29-year-old NL Cy Young Award winner Jake Arrieta, are in the midst of their primes.
The Cubs' window is just opening—wide. Does that mean the Cardinals' is closing?
Maybe not. Mixed in with the older pieces are outfielders Randal Grichuk and Stephen Piscotty, promising rookies in 2015 who are currently slotted into starting roles. Second baseman Kolten Wong, an NL Rookie of the Year finalist in 2014, is 25. And 24-year-old right-hander Carlos Martinez was an All-Star last season before a shoulder strain shut him down.
St. Louis' farm system isn't the game's most loaded—Bleacher Report's Joel Reuter ranked it No. 19—but there are some intriguing pieces in the pipeline, including 21-year-old right-hander Alex Reyes.
Mostly, the Cardinals can stand on their reputation for developing talent, plugging holes as needed and perennially sitting at or near the top of the NL pecking order.
This franchise hasn't suffered through a losing season since 2007, made it to the NLCS every year between 2011 and 2014 and won a pennant in 2013 and a World Series in 2011. Players have come and gone. The success has endured.
Call it good fortune, call it design, call it the Cardinal Way. But dismiss this team and its chances at your peril.
While Heyward's remarks aren't likely to spawn a beanball blood feud, they'll no doubt give St. Louis added motivation when it hosts the Cubs for the first time of the season on April 18.
After Heyward's press conference and Matheny's rebuttal, Cardinal Nation succinctly summed up the feelings of, well, Cardinal Nation:
The Cards took an expensive swing at Heyward and missed. Then he took a shot at them and they fired back.
"I think "Mo" [general manager John Mozeliak] did a great job of aggressively trying to push the envelope, the way this organization has done before, but still be responsible," Matheny said, per Hummel. "But you have to have the other guy play along."
Now, this rivalry has a few more months to simmer. Maybe we'll even get a little more spice sprinkled on top. Then prepare to dig in, baseball fans—because this promises to be one tasty storyline.
All statistics current as of Dec. 20 and courtesy of Baseball-Reference.com unless otherwise noted.