SCOTTSDALE, Ariz. — The line drive that broke Madison Bumgarner’s pitching hand in March, on the final day of spring training, was a crushing blow from so many angles. The one that really ate at manager Bruce Bochy was how well the Big Fella was throwing.

Bumgarner had 30 strikeouts in 21 Cactus League innings, a sign that he was fully recovered from the dislocated pitching shoulder suffered in a motorbike crash the year before.

Now, after another injury-marred season, the process starts anew. After watching Bumgarner throw his first bullpen of 2019 on Wednesday, Bochy said, “Bum threw well. You could tell he came in ready.”

The difference this year is, Bumgarner will be pitching not only for the Giants, who have to make a colossal financial decision on their future with the left-hander, but for all the teams that might consider trading for him in July or signing him next winter.

All of those teams surely want the answer to one huge question:

What happened to Bumgarner’s fastball?

Bumgarner never had white-lightning heat that made hitters’ knees tremble. At its fastest, it averaged 92.8 mph in 2014 and 2015, according to FanGraphs. It dipped to 91.5 in 2016, 91 in the Year of the Motorbike and 90.9 last year upon his return from the broken hand.

Moreover, hitters crushed it last year, batting .299 against the four-seamer: 43 points better than the year before and 63 points better than in 2016.

Not surprisingly, Bumgarner moved away from the pitch in a way he never had in his first eight big-league seasons, throwing the fastball a career-low 34.2 percent of the time. He compensated by throwing more curveballs and changeups, while keeping his cutter rate the same.

When asked by The Chronicle about his declining fastball velocity, Bumgarner suggested his injuries played a part. More specifically, rushing back from the injuries, which he does not regret. It doesn’t mean he was still hurt. He just sacrificed the extra rehab time that might have advanced him to Peak Bumgarner because the team needed him.

“You want to get back on the field,” he said. “When you feel good enough to compete, you’re going to be back.”

Bumgarner considered his velocity “normal” in 2017 until the bike accident.

“Then I got hurt and rushed back as fast as I could,” he said, “too fast probably both times to be 100 percent.”

His velocity did not fall off a cliff the past two seasons, but any pitcher will agree that a fastball’s “life” is equally important and can become a casualty of injury.

Bumgarner was not in a mood to dissect it and he never professes to care how hard he is throwing.

His mantra on velocity: “I don’t think it’s the be-all and end-all.”

That is truer for a pitcher like Bumgarner, who still has a panoply of ways to fool hitters, starting with a good array of cutters, curveballs and changeups, and a beguiling three-quarter motion that allows him to hide the ball behind his mountainous body.

The cutter has always been a big pitch for Bumgarner, even when he has a good fastball.

Still, people around the game have wondered if a precipitous decline in Bumgarner’s peripheral stats in 2018 bore some connection to his declining fastball velocity and usage.

His strikeouts per nine innings fell to 7.6, his lowest rate since 2010. His fielding-independent pitching, an ERA-like number based on walks, strikeouts and home runs, rose to a career-worst 3.99 while his WHIP was 1.24, again his worst since 2010.

The pressing issue is whether Bumgarner can reverse the trend merely through a season of good health, or whether he needs to adapt after throwing more than 1,700 regular-season and postseason innings before his 30th birthday.

Either way, pitching coach Curt Young does not see a burning need for more heat from Bumgarner.

“Bum knows how to pitch and he understands what he’s going to do with his fastball,” Young said, “whether it’s to push guys back, get them out away, to elevate and change their eyesight or, if he needs to come into the zone, he knows he has to keep the baseball down.

“He’s good enough out there to know what he wants these hitters to hit, and if it’s not his fastball, it’s not going to happen. He’s such a fantastic strike-thrower, he throws strikes with his non-fastballs the way other guys throw strikes with their fastballs.”

Like any pitcher, Bumgarner’s feel for the fastball changes from game to game. His varied arsenal allows him to adapt, and he has enough in his holster to dissuade him from stubbornly throwing the same pitch time and again when hitters are on it.

But he does stubbornly refuse to acknowledge, at least publicly, that this is even an issue.

“If I’ve got to throw all fastballs or no fastballs, I’m going to do whatever I need to do to get guys out,” he said. “I’m not trying to say, ‘Well, I need to up my fastball percentage here and throw one for the fun of it.’

“Whatever I see fit to get guys out.”

If Bumgarner can pitch in this year’s exhibitions the way he did last year — without the film noir ending — a lot of folks in black and orange will be relieved. For now they have one bullpen session to go on. Bochy liked what he saw. So did the kid who caught him, Joey Bart, who said Bumgarner hit his glove with nearly every pitch.

When the session ended, Bumgarner told Bart he was glad to get his first one out of the way.

“That,” Bart later told reporters, “was a pretty good ‘first one.’”

Henry Schulman is a San Francisco Chronicle staff writer. Email: hschulman@sfchronicle.com Twitter: @hankschulman