McGwire, after all, was a widely presumed participator in the performance-enhancing drug environment. He had no prior coaching experience. And now he was bringing his baggage to the Cardinals clubhouse?
It seemed fair to wonder if McGwire would be more of a distraction than a help.
But La Russa didn't waver.
"I keep hearing that I did it to rehabilitate him and do a friend a favor," La Russa recently told Dan Patrick in an interview that ran in Sports Illustrated. "That's an insult. When you're a manager, the organization has entrusted you with the responsibility for its team."
And La Russa knew what most did not, could not, would not -- that there was much more to McGwire than the home-run heroics and the steroid discussion. There was a man who learned, over the course of his career, to study the art of hitting and yearned to pass that knowledge on to the next generation.
Because of foot and heel injuries, McGwire played just 74 games over the course of the 1993 and '94 seasons. But this still proved to be a productive period for him, because he used his time on the pine to refine his mind.
"I believe there's a reason things happen to you in your life," McGwire said. "So I said, 'OK, why are these injuries happening to me?' It was the first time in my life that I had to sit back and actually watch the game of baseball. I had always been playing it and never actually watched it."
As he watched, McGwire noticed the nuances of the battles taking place between pitcher and hitter. He developed a greater appreciation for patience and plate discipline and of the video viewing that Tony Gwynn had begun to make mainstream.
The stain on McGwire's career is that he illicitly built up his body. The less scandalous side of the story is that he also built up his hitting acumen, and of this La Russa took note.
"Mark was really talented [early in his career], but he was absolutely clueless about hitting," La Russa said. "Later in his career, he got brilliant."
McGwire does not refute the notion.
"When I decided to get into coaching, that's what I started to preach to the young kids," McGwire said. "There's more to it than seeing it and hitting it, which you do have to do. Mentally, you have to be prepared, and that starts at 2 o'clock in the afternoon, long before we take the field, and then there are adjustments that are made during the game."
A hitting coach, like a manager, is ultimately only as good as his personnel, and the 49-year-old McGwire has worked with some truly talented hitters in Albert Pujols, Matt Holliday and Lance Berkman, among others.
He has also, however, succeeded in helping less-established players like David Freese and Allen Craig capitalize on their potential. He has put guys like Pete Kozma and Matt Carpenter in position to find their big league footing. He has assisted Yadier Molina's maturation from a catcher with a reputation solely on the defensive side to a legit middle-of-the-order presence who has led the Cards in batting average each of the past two seasons.
"The interesting thing about his evolution as a coach," said general manager Jon Mozeliak, "is his passion to work with hitters. He's evolved in how he communicates, how he works with hitters. But his desire and work ethic are a rare commodity, as far as how much he dives into this."
Mozeliak admitted he didn't know exactly what he was diving into when McGwire was hired. In early 2010, Mozeliak told reporters that he had even begun to put together what he called an "exit strategy" to find a replacement hitting coach if McGwire didn't open up about his past before Spring Training. A confession was, essentially, a prerequisite for the position, because the Cards wanted McGwire to handle the media demands and distractions before the club reported to camp.
Two and a half months after his hire, McGwire came clean, offered his apologies and then went to work. And while a confession obviously didn't put him in the good graces of the Hall of Fame voters, it has allowed him to move on with his life and give something back to the game.
In the three seasons since McGwire took over his post, the Cardinals have led the NL in batting average (.269) and on-base percentage (.337), ranked second in runs (2,263) and fourth in slugging percentage (.416). By any measure, they have been one of the most formidable offensive units in the sport, and McGwire, with a 2012 assist from John Mabry, deserves a measure of the credit.
Where you really see McGwire's influence, beyond the numbers, is in the words of those he works with. His players repeat his mantras about being patient, not chasing, limiting strikeouts (among NL teams, only the Phillies have struck out less over the last three seasons) and, as McGwire likes to put it, "keeping the merry-go-round going" in a big inning.
"That starts with Big Mac," said Freese, "and what he preaches."
The Cards' signature moment in this October run to the World Series was a direct result of McGwire's tutelage. Drew Storen shut the Cards down in Game 4 of the NL Division Series by being, in McGwire's words, "effectively wild" with his slider. McGwire instructed his troops to pass on the pitch if they faced Storen in Game 5, and, sure enough, the ninth-inning rally that night was keyed by Molina and Freese each drawing a walk on 3-2 sliders that were trickily tempting.
"I love seeing frustration in the opposing pitcher, and I saw that with Storen," McGwire said. "I love seeing our hitters work the count. When you work the count and see as many pitches as you can each at-bat, it sets the tone for the rest of the lineup, and it sets the tone for the game."
The tone surrounding McGwire's work is an overwhelmingly positive one now. Certainly more positive than when he was hired three years ago.
So, is this a story about vindication, about repairing a reputation? Perhaps.
At its core, though, this is a story about a great hitter who simply couldn't shake the game he loves and has proven great in another area.
"I didn't really have any expectations for it," McGwire said. "I didn't know what it would be all about. But I knew I wanted to do it, because I knew I had a lot of knowledge to pass on. I enjoy it, I love it and, hopefully, I'm around it until the day I die."