Simple: "I think, in general right now, I'm not seeing the ball as well as I could be."
Less simple: "I'm not getting to a good balance point in my setup when I load."
In layman's terms, Duffy is not maintaining his balance when he cocks his hands and begins to stride forward to gather momentum for his swing.
"That balance point is kind of where I gather my information for whether I want to swing or take," Duffy added. "Since I'm not getting to that kind of balance point right now, I'm not giving myself a good chance to get good information from the ball. I'm jumping at it. I'm sure you [reporters] have seen it. I'm swinging at a lot of offspeed pitches that are pitchers' pitches early in the count when I don't necessarily have to."
Duffy observed that it doesn't take much for a ballplayer's production to fluctuate "when you're talking that the difference between a base hit or a popup is a quarter of an inch [on the bat]."
As he promised to do early this week, manager Bruce Bochy left Duffy out of the lineup for Monday night's series opener against the Arizona Diamondbacks to give the 25-year-old more time and energy to refine his swing.
Duffy indeed took extra batting practice hours before the game began. Bochy, who also wanted Duffy to use his day off to clear his mind and relax, said he'll return to the lineup Tuesday.
Kelby Tomlinson made his first regular-season Major League appearance at third base in Duffy's stead. He played four games at third last year with Triple-A Sacramento.
Chris Haft is a reporter for MLB.com. Read his blog, Haft-Baked Ideas, follow him on Twitter at @sfgiantsbeat and listen to his podcast. This story was not subject to the approval of Major League Baseball or its clubs.