Jonathan Lucroy comes to the A’s with some baggage.

Namely, a massive book of scouting reports on opposing hitters, phone-book-sized. A’s coaches approximate the catcher’s tome with gestures, and each time it gets bigger in their estimations.

The technology is decidedly old-school.

“It’s a middle-school Trapper Keeper,” Lucroy said. “I have an insert for all 30 teams and scouting reports for every team going back seven years.

“I have my own system. I break ’em down as far as I can get to. There is a place for the sabermetrics and the analytics, and I have that, but without getting too much into it, I break down hitters by what they’re good at, what they’re bad at and what our pitchers can do to get them out.”

Lucroy is a catcher’s catcher, a two-time All-Star who puts in obsessive levels of work to ensure that he calls a good game and does everything possible behind the plate to help his team win.

He learned from one of the best: former A’s catcher Jason Kendall, a noted drill sergeant of a player who was at the tail end of his career in 2008 when Lucroy was still in the minors.

“I took Jonathan under my wing big-time my first year in Milwaukee. They brought him to camp from A ball because someone got hurt, and he just followed me around like Kurt Suzuki did in Oakland,” Kendall said. “He ran through the system fast and boom, knocked me out of a job, like Suzuki did. I couldn’t be more proud of both of them. They both show you don’t have to be a big old catcher — they’re both a similar size to me. You have to be athletic, and more than anything, you have to know how to run a game.

“Bottom line is: He cares. A lot of guys don’t get a hit their first or second time up and (give up on) the catching, or they show up at 3:45 p.m., but not Lucroy. And if you show pitchers you care, you’ve got them in the palm of your hand. He’s just a great addition for them.”

Lucroy, 31, has had some fine years at the plate — he hit .292 with 24 homers and 81 RBIs in 2016, and his lifetime average is .281. Make no mistake, though: The A’s signed him to a one-year, $6.5 million deal this spring to help their pitching staff, particularly the young starters, who’d struggled through the first two weeks of camp.

Lucroy has had an impact already: In the first four spring games he caught, Oakland starters allowed five earned runs in 222/3 innings, a 1.99 ERA.

“So far, amazing,” pitching coach Scott Emerson said. “Lucroy’s energy and his excitement to just catch and call a game are the best I’ve ever seen, and he’s been here two weeks. It’s a massive difference for those (pitchers) — just the presence and the name, everyone knows who he is and his leadership ability. He’s everything you look for in an everyday catcher.”

One National League scout who has seen Lucroy throughout his career in Milwaukee, Texas and Colorado called him the perfect fit for a team with a young rotation. “He’s some kind of leader,” the scout said. “He comes in and makes such a difference for pitchers, it’s a totally different atmosphere. His game management, game-calling, working with pitchers — it’s all outstanding.”

The job verges on art for Lucroy, and it starts with in-depth knowledge of the pitchers. Not just their stuff, but what they’re like as people, because he has to be part therapist, part authority figure.

“In this world of analytics and sabermetrics, the biggest thing for me is personalities — what they’re like, how they react — to enable me to get the very best out of them every time they’re on the mound,” Lucroy said. “You have to be a mix of things. There are guys you can motivate a little more ... firmly. There are some other guys you can’t, you have to try something different.”

Lucroy watches at least two hours of video before each series, and he has broken down himself, too, when he studies hitters’ tendencies. He picks up others’ weaknesses, and he looks at his own to see what he can change at the plate. Plus: He’ll occasionally pick up some offensive tips he can use during his marathon study sessions.

He’s eagle-eyed during games, trying to be alert to any possible adjustment that can be exploited. How did a hitter react to a certain pitch? Did he move where he’s standing in the box? If a batter does something unexpected, it goes straight into the memory bank, and, perhaps, the Trapper Keeper.

“Kendall told me nine years ago that it took him seven years in the big leagues to really be able to call a game. At the time, I didn’t understand him,” Lucroy said. “Now I can see what he’s talking about. When you’re around a little but you’ve seen so many things and you start to see the game differently. You see things from a different angle.”

Catching isn’t challenging just mentally, of course — it’s by far the most demanding position physically. Lucroy is 6 feet and listed, optimistically, at 200 pounds. He tends to drop weight during the season, so he has to train all the harder.

“I do a lot of recovery stuff,” he said. “I eat as well as I possibly can and I have to eat a lot because I burn a lot of calories. I have to work out a lot to maintain my body mass. I have to be flexible and stretch.

“I have some mileage on me, I’ve caught a lot of games in my career. I’ve been fortunate enough to stay pretty healthy. Some freak stuff has happened, but I’m grateful I’ve been mostly healthy.”

For Lucroy, it’s all worth it.

“I fully 100 percent enjoy it,” he said. “Catching, being behind the plate, trying to get these guys through a game, is something I love to do. I’m glad my dad made me a catcher when I was 10 years old.

“I played first base a few times in my career and it wasn’t fun. It was boring. As a catcher, you have to be locked in every pitch, every inning, every game. You can’t lose focus. It’s an extreme challenge, and a lot of people can’t handle it. A lot of people can’t handle the amount of information you have to take in, the amount of perception you have to have, the amount of attention to detail and knowledge of situations. I fully relish it and enjoy it.

“It’s an honor to be behind the plate.”

Susan Slusser is a San Francisco Chronicle staff writer. Email: sslusser@sfchronicle.com Twitter: @susanslusser

A’s-Giants

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