Why Giants' Matt Duffy -- not Joc Pederson or Kris Bryant -- is NL's top rookie

Jorge L. Ortiz | USA TODAY

SAN FRANCISCO – The player who eventually replaced Pablo Sandoval as the San Francisco Giants’ third baseman carries around a dog-eared self-help book, leaves himself reminders to eat – lest he wither away – and has been tagged with a nickname that hardly fits his physique.

If the Giants had requested the exact opposite of their once-beloved Panda from central casting, they would have been sent Matt Duffy.

The 6-foot-2 rookie, who may push the scales up to 175 pounds after a big meal, has dispelled any yearning for the rotund Sandoval with such consistent and unexpected production, the Giants didn’t bother seeking an upgrade at the trade deadline.

“We look at him as our third baseman now and for the foreseeable future,’’ general manager Bobby Evans said.

Those plans may eventually change, considering Duffy began the season as a utilityman and doesn’t exactly fit the profile of the prototypical third baseman. His Duffman nickname – based on the Simpsons muscular character – was clearly inspired more by his surname than his slender build.

But the Giants may be hard-pressed to find equal production, let alone similar value.

Duffy, 24, heading into Tuesday, is second among all rookies in wins above replacement (3.4), has the second highest batting average (.301) and the seventh-highest on-base-plus-slugging percentage (.797) among National League rookies.

He even compares closely to highly touted rookies Joc Pederson of the Los Angeles Dodgers and Kris Bryant of the Chicago Cubs, power hitters who have attracted national attention. Bryant trails Duffy in OPS, slugging percentage (SLG) and wins above replacement (WAR) and Pederson trails in SLG and WAR.

“They’re great baseball players, exciting baseball players,’’ Duffy said of his rookie of the year competitors. “To even be lumped into a conversation or even a footnote with them is exciting.’’

Duffy is perfectly aware he wasn’t supposed to be here, not in the role of starting third baseman and No. 3 hitter for the defending World Series champions. The Giants had traded for Casey McGehee to replace Sandoval, who signed a five-year, $95 million contract with the Boston Red Sox in the offseason, eschewing a similar offer from San Francisco.

Duffy earned a spot on the team as an infield backup only after batting .361 in his first major league training camp.

“He was our most productive offensive player in spring training,’’ Evans said. “He never let up.’’

That was the continuation of a remarkable transformation for a player who batted .254 with zero home runs in three college seasons at Long Beach State, and who was drafted in the 18th round in 2012 to provide the farm system defensive depth in the middle infield.

The offensive makeover actually began between Duffy’s sophomore and junior seasons, when he came under the tutelage of coach Benny Craig in the wooden-bat Cape Cod league. Craig suggested Duffy stand farther away from the plate to avoid getting jammed and that he incorporate a leg kick to improve his load, showing him video of the impact such a change had on Jose Bautista’s career.

After a week and a half of feeling out his new swing, “It clicked one day and it was like, ‘Wow, that’s how it’s supposed to be,’’’ Duffy said. “I’d face a guy throwing like mid-90s and the ball looked like it was mid-80s.’’

Duffy went from filler to All-Star in the league, finishing third in batting average at .348.

Craig said Duffy’s outstanding hand-eye coordination and his analytical mind allowed for the modifications to set in quickly.

“Matt’s just a grinder,’’ Craig said. “It’s funny he went to Long Beach because they’re the Dirtbags. He’s a baseball dirtbag.’’

A digestive ailment just before his junior season forced Duffy to drop 10-12 pounds he could ill afford to lose, down to the low 160s, and he wound up batting just .244 that season.

The Giants still liked his defensive skills and competitive at-bats enough to draft him, and at Craig’s urging Duffy picked up Harvey Dorman’s “The Mental Keys to Hitting’’ before his first pro spring training. The book has become Duffy’s hitting bible – he has read it about 10 times – and he still turns to it for reinforcement when he falls in a slump.

“I think that book is 12 chapters or so of saying the same thing over and over,’’ said Craig, “trying to brainwash you: You can only control so much. Come game time, trust your swing, let your eyes take over, let them be your No. 1 tool.’’

With that approach, Duffy batted .303 with an .832 OPS his first full pro season in 2013, then really caught the Giants’ attention by winning the Class AA Eastern League batting title with a .332 average last season. He was called up in August and included in all the postseason rosters.

Hoping to improve his strength, Duffy went through great efforts to gain weight in the offseason, setting an alarm so he would remember to eat something every hour, even if it was just a banana, a protein shake or an energy bar.

“If I ever felt hunger, I’d waited too long,’’ said Duffy, who did gain about 10 pounds to 180 but is now down to 170-175. “It was kind of a chore being full all the time. It definitely made eating not as pleasurable, but I understood what it was for and I knew I was going to be better because of it.’’

When McGehee faltered so badly he was demoted to Class AAA in late May, Duffy took over at third – a position he played in only three games in the minors – and never let go. He has grown into the position while demonstrating remarkable offensive consistency, batting .313 in May, .313 in June and .319 in July. McGehee, making $4.8 million – or $4.3 million more than Duffy – was released July 8.

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Two weeks before that, manager Bruce Bochy moved Duffy to the third spot in the lineup ahead of Buster Posey, and has kept him there since. Duffy is hitting .312 with an .811 OPS in the 3-hole.

“He just kept coming up with big hit after big hit,’’ shortstop Brandon Crawford said. “He was hitting .300 when Casey was really struggling, so everybody could kind of see there was probably going to be a change. He has hit in the middle of the order for us consistently.’’

There is some concern that Duffy may wear down in the season’s final two months, especially with the Giants facing a stretch of games in hot-weather cities. He acknowledges the need to hydrate and eat frequently to keep his fast metabolism fueled.

But Bochy said he’s not among those stunned by Duffy’s production, which includes nine homers, 48 RBI and a robust .457 slugging percentage. Bochy points to Duffy’s athleticism, his opposite-field approach and ability to turn on inside pitches as evidence he’s legit.

“I thought this last year: This kid’s going to hit for more power. I really thought that, watching his swing, his great balance,’’ Bochy said. “He rotates on the ball well. He’s a rotation hitter, and he has some strength. I thought he would start hitting, not many more home runs but doubles, and he’s got a few home runs too. I’m not surprised.’’