In just his 10th Major League at-bat, he hit the final regular-season home run in old Busch Stadium. After a year in which he struggled against left-handed pitchers, Duncan cranked a key pinch-hit homer off a lefty in the National League Championship Series as the Cardinals charged toward a World Series title. And he put up numbers as a rookie that looked a lot like what 2006 NL MVP Ryan Howard did a year before his 58-homer outburst.
Duncan was the second-most dangerous hitter on the Cardinals for large chunks of 2006. A player who always had the ability to hit the ball ridiculous distances finally started to harness that ability, catching nearly everyone off guard -- except, perhaps, himself.
"I wasn't surprised," Duncan said. "I knew I had it in me. I think I was just a little more consistent throughout the whole second half than I had been before. But I knew that I was capable of being a good hitter."
Yet, thanks to some ill-timed miscues with the glove, Duncan rates as a question mark rather than a legend in the making to many fans and observers. They wonder whether the 25-year-old can handle playing in the outfield on a daily basis, rather than marveling over the offensive pyrotechnics Duncan produced in 2006. Ironically, for a player with such offensive talent, the first word many people associate with his name is defense.
The offensive talent, though, is tough to ignore. Duncan batted .293 in 280 big-league at-bats following a midseason call-up from Triple-A Memphis. He posted a .363 on-base percentage and slugged a robust .589. The 6-foot-5 slugger smacked 22 long balls in 90 games. Duncan simply was a holy terror at the plate.
In fact, he hit like he'd never hit before. Duncan's 22 dingers in half a season in the Majors surpassed his previous full-season total in the Minors (21, at Memphis in 2005). The batting average and slugging percentage likewise were personal bests.
By contrast, Howard hit 46 Minor League home runs in 2004 before going deep 22 times in the bigs in '05. Power came quickly for Howard, whereas it developed in fits and starts for Duncan, a supplemental first-round pick way back in 1999.
"It's hard for me, being in the Minors for seven years, and then all of a sudden I'm there for a half season and people compare me to Ryan Howard," Duncan said. "It's hard for me to understand that. The most home runs I ever hit in my life was last year. The most I ever hit in a full year was like 21.
"He's been a legitimate power hitter ever since he came into the Minor Leagues. He's always put up astronomical numbers throughout the Minor Leagues. So there's no surprise when he did what he did last year. But for me, it's been a grind. I've come a long way since I signed, and nothing has really come easy. It's been a real gradual process for me."
So what's to come for Duncan in 2007? Can he make the huge leap that Howard did, erupting from 22 homers as a rookie to 58 in his first full season? Or will he look more like the promising but rough young hitter who never quite translated massive raw power into consistent production?
"I wouldn't project him out," said Cards hitting coach Hal McRae. "I just hope that he continues to improve, which I think he will. I don't think it serves any purpose to project him out and say if he had been here all year and he had had 'X' number of at-bats, he would have done thus and such."
One encouraging sign going forward is Duncan's steadily improving plate discipline. As a young pro, the lefty swinger was a hacker. But he started to turn the corner in 2004, ratcheting up his walk rate while slightly cutting back on the strikeouts.
Duncan drew a walk for every 9.3 at-bats in the Majors in 2006. He's made it a priority to wait for his pitch -- not to be passive, but to make sure he gets the offering he wants. He credits Steve Balboni, the hitting coach at Double-A Tennessee, with starting the transition and McRae for helping him keep it up.
"As soon as I started developing [selectivity at the plate] is when I really started becoming a better hitter," Duncan said. "Because you can have all the talent in the world, and if you're up there just chasing everything, you're not going to get anything."
McRae also emphasizes an approach that in auto racing they would call "go slow to go fast." Both coach and player want to make sure that Duncan doesn't overswing -- that he doesn't try to hit home runs. When you have the natural strength that Duncan has been blessed with, all you need to do is swing solidly and smartly. The ball will travel.
"Sometimes, when you've got power, you just try to crank everything, and you're not going to consistently put the ball in play enough to hit a lot of home runs," Duncan said. "So last year I tried to cut my swing back. Instead of swinging 100 percent, just take a nice easy swing. You surprise yourself when you do that, because you put the ball in play more and you start putting the barrel on the ball more. And next thing you know, the ball is going out of the ballpark."
He's talked with everyone from McRae to Jim Edmonds to former St. Louis slugger Mark McGwire about hitting. Duncan has a great trait for a young player: He knows how much there is that he doesn't know. He tries to glean something different from everyone, whether it is mechanical tips, advice on preparation and game planning or blocking out distractions.
"That's a big thing that [McGwire] talked about, is how to block everything out," Duncan said. "All that matters is that one at-bat. You're up there competing against the pitcher that one at-bat. That's a good way to go about it. It's a good way to be consistent. A lot of times you can let one game affect a whole week if you're not careful."
Duncan has taken that advice to heart at the plate, but he still hasn't mastered the same approach in the field. And that opens the door to questions about his ability to play every day.
Manager Tony La Russa insists that with repetitions, Duncan will be an average outfielder or better. Duncan believes he has the physical skills he needs to do just that. What he needs to do, he says, is to relax.
Duncan fully acknowledges he wants and needs to improve as an outfielder. But he also argues that a couple of extremely high-profile gaffes in the World Series led to a perception of him being worse than he actually is.
"I thought there was a month or five weeks where I played really good defense," he said. "But being inexperienced out there, when I made a couple mistakes, it kind of snowballed. I know physically I'm capable of being a good outfielder. I think I have the tools to be a good outfielder.
"I think the biggest thing for me is just finding a way to get comfortable and fighting nerves. When I was relaxed and comfortable, everything was fine. But it seemed like when I made some mistakes, and the more people talked about it, the more I pressed. And I put more pressure on myself to be good out there, and that made things worse."
It was no fun for Duncan to hear constantly about his shortcomings, rather than his strengths. But he accepts it admirably.
"I'm glad I went through it," he said. "That's part of it. You play on a winning team and everything is going to be magnified. If we were in last place and I was dropping balls, no one would [care]. I'd rather be on a winning team and have people criticize the mistakes I've made, because that means you're in the hunt for things."
So he'll take tons of repetitions in the outfield this spring, working more and more on making it all come naturally. And he'll try to apply the lessons learned about hitting to the area of his game where he needs the most work.
And in the meantime, the Cardinals hope he'll keep mashing the ball. Perhaps enough so that the tone of the conversation will change, and more people will take note of what Duncan can do than what he can't.
Matthew Leach is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.