This is complicated stuff he's talking about, and he needs a prop.
He's trying to explain his peculiar career with the Royals -- a career that has teetered on the edge between success and failure for three rocky seasons.
Bannister was one of the best rookie pitchers in baseball in 2007. He was called a fluke in 2008. And now, in 2009, he's found redemption by posting a 3.59 ERA in 20 starts -- the 13th-best ERA in the American League as of Wednesday.
And that's where the ball and the locker and Bannister's impromptu clubhouse pitching lesson comes in.
He's talking about physics and angles and spin, and at that moment, he drops the ball.
"When you're talking about a fastball or a cutter or a sinker," Bannister says, "it can only sink at the rate of gravity."
He's starting to get technical now, sounding more like a math professor than a pitcher.
"He's smarter than the average person," says teammate Bruce Chen.
But here's what Bannister wants you to know.
He's at home in the numbers, and he thinks he's found a secret to his 2009 success. He attributes part of that secret to the Pitch f/x technology on MLB.com's Gameday Premium.
A few years ago, high-speed cameras were installed in all Major League ballparks, Bannister says. The technology can quantify numbers that hadn't really been quantified before.
Technically, the Pitch f/x feature spews out three numbers with every pitch. The simple number is the pitch's velocity. The other two are a little more complicated. The "Pitch-f/x" value is the measurement of the distance between the location of the actual pitch and the calculated location of a ball thrown by the pitcher in the same way with no spin. The "Break" quantifies the distance in the given trajectory of a pitch compared with a pitch that was thrown in a straight line. In short, a big, loopy curveball will have a large amount of "Break."
For a student of the game such as Bannister, the technology provides a digital treasure chest of digestible information. And slowly, solutions started to form in his head -- solutions that reshaped his pitching philosophy.
"It wasn't where you throw a pitch in the strike zone," Bannister says. "It's the actual vertical rise or sink on the ball as it's getting to that location in the strike zone, and that's exactly what Pitch f/x shows."
He was able to analyze specific numbers and apply them to his pitching.
"Quite unsuccessfully at first," he admits. "But I think now I've really come to some good conclusions regarding the data. I'm top five in the American League in ground-ball percentage now, which is just proof that the system works."
Bannister's story is well known in baseball's sabermetrics community. He'll often talk about Bill James, a pioneer in the world of advanced statistics.
"If Bill James had a 90-mph fastball, he'd be me," Bannister says.
Bannister grew up in and around baseball clubhouses -- his father, Floyd, played 15 seasons in the Majors -- and fell in love with the game.
After a successful career at the University of Southern California, Bannister was selected by the Mets in the seventh round in the 2003 First-Year Player Draft. It was with the Mets organization that Bannister started finding meaning in numbers.
Bannister recalls Rick Peterson, the Mets' pitching coach at the time, talking about pitch counts. It was simple math -- "If you get ahead of a guy in an 0-2 count, his batting average goes down," Bannister says -- but the message stuck.
"It got me intrigued into how different things affect my future success in this game," Bannister says. "It's been a process, because nobody is out there using sabermetrics as a tool in player development.
"I kind of feel like I'm a pioneer in that aspect of the game. That every fifth day when I go out there, the Major Leagues is kind of my way to apply this stuff and see if it can be used in the future for developing players."
Bannister sees flaws in the traditional way pitchers are judged. An ERA is a good measurement of success, but it's limited, he says.
To get a real indication of his effectiveness, Bannister looks at other stats. He looks at BABIP -- batting average of balls in play -- and FIP, which takes fielding out of the equation and measures pitchers based on homers allowed, walks, hit batters and strikeouts.
"I think people universally agree -- in the sabermetric community and the fan community and in the media community -- that sabermetrics are effective at identifying successful baseball players and ways to win this game," Bannister says.
His short career has validated his arguments.
Bannister was 12-9 with a 3.87 ERA in 2007, and on the surface, the numbers flashed potential. He was just 26 and one of the best young starters in the league.
But Bannister saw something different. He struck out just 4.2 batters per nine innings, and his BABIP was .262, well below the league average. He will be the first to admit that he was lucky.
So in 2008 he tried to change his style. He started throwing more four-seam fastballs to improve his strikeout totals. He thought he'd strike out more people, make more guys swing and miss, and that would help combat his rising BABIP.
It didn't quite work that way.
Bannister imploded in 2008, with a 9-16 record and a 5.76 ERA. His strikeouts did rise a little, but all those four-seam fastballs turned into fly balls -- and some of them left the ballpark. He gave up 29 homers, and many began to wonder if he was a one-year statistical anomaly.
They wondered even more when Bannister was lit up in Spring Training this year. He started the season with Triple-A Omaha, and with nothing to lose, he ditched the four-seam fastball. He studied Pitch f/x, looking for ways to get more ground balls. The answer was simple: He had to start throwing his cutter more -- a lot more.
And it's working.
He's getting ground balls, and his ERA is down to 3.59. But the important thing, he says, is that the other numbers back up his success. He's hasn't been lucky. He's just been good.
Standing by his locker, Bannister starts to wrap up his lesson. There's a crowd now. He's talking about FIP and BABIP and the numbers behind the numbers. A few feet away, Chen stops. He's listening, too.
"He has helped me with the Pitch f/x," Chen says. "I'm not very much into the percentages, but if he continues to have success, then that might be something I need to take a look at."
Bannister knows that other players might not be as easily convinced. But if any player -- or any person -- wants to talk numbers or advanced stats or Pitch f/x ratios, Bannister is always up for it.
"I think it'll be a tool used for player development as soon as somebody can explain how it can be used," he said. "I don't think guys are going to risk their careers trying to follow something they don't understand. That's why I think what I'm doing is fairly unique. I'm pretty much doing it on my own as a way to get better."
Rustin Dodd is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.