SAN FRANCISCO — Of all the words in the dictionary, these are the five that most warm the hearts of baseball fans: “Pitchers and catchers report Tuesday.”

The Giants’ attempt to recapture the World Series trophy begins this week in Scottsdale, Arizona (the A’s start a day later in Phoenix), with the first spring training game slated for Feb. 24. As usual, one man squats in the center of everything for San Francisco — Buster Posey, the Giants’ starting catcher, likely cleanup hitter and unofficial franchise face.

“He’s one of our leaders, our core players. And those are the guys you lean on, depend on, both on the field and in the clubhouse,” manager Bruce Bochy said Friday in a media warmup for Saturday’s FanFest at AT&T Park. “We had three championships with him behind the plate and handling this staff. So he plays a critical role.”

There is no questioning Posey’s importance to the Giants. But as the team regroups from a 2016 season that included a prolonged second-half stumble and an unheard-of (under Bochy’s reign, anyway) playoff exit, even the catcher bears a question mark. What, exactly, happened to Buster Posey last year?

It’s not like he disappeared in 2016. Far from it. Posey led the Giants in hits (155) and runs (82), and logged a highly respectable batting average, on-base percentage and OPS (on-base plus slugging percentage) of .288/.362/.796.

But Posey simply didn’t have the pop we’re accustomed to seeing. His 14 home runs were a career low (excluding his injury-shortened season in 2011), and his 80 RBIs were not MVP-quality, which is the bar Posey set when he won the National League award in 2012.

More to the point, Posey’s power numbers declined as the season progressed. His slugging percentage went from .462 in July to .407 in August to .363 in September/October.

He hit his 12th home run against the Padres on July 16, the Giants’ second game after the All-Star break, then went deep exactly twice over his final 69 games, including five in the postseason.

Embedded in there somewhere was a stretch of 49 consecutive games without a dinger. San Francisco went 20-29 in those games.

Fair or not, it’s hard to imagine the Giants contending for a title this season if Posey goes 49 games without a home run.

“I don’t know. I don’t know exactly what the explanation was,” Posey said Friday, appearing genuinely perplexed. “Looking forward to getting out and getting after it this year.”

Bochy suggested that opposing pitchers were “being careful with him” down the stretch last season. Posey, citing an analytics piece that someone showed him, noted that his hard-hit rate remained as high as ever.

“So if I look at that, that tells me that I was probably hitting too many balls on the ground,” Posey said. “Maybe that could be something mechanical. More than likely it probably is. So hopefully there’s an adjustment I can make where I can keep that consistent hard-contact rate, but maybe get a few more balls in the gap or better.”

All of that makes sense. But among those who have watched Posey closely over his seven MLB seasons, another theory emerged in 2016. The guy looked increasingly tired as he logged 122 games behind the plate, the most of his career.

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