SCOTTSDALE, Ariz. — The minute reporters were allowed into the Giants’ clubhouse Monday, the voice of country singer Brett Young filled the room. In an uproarious coincidence, given the news of the day, he was singing, “In Case You Didn’t Know.”

That should be the title of the book Madison Bumgarner writes about his secret life as a championship rodeo roper.

Bumgarner’s former teammates and manager, some he has known for more than a decade, swore on a stack of Willie Nelson albums they had no idea Bumgarner’s mamma let her baby grow up to be a cowboy — at least a money-making one — who for years has roped steers under the alias Mason Saunders.

“This is the first I know of Mr. Saunders,” former manager Bruce Bochy said. “I’m a little disappointed he didn’t call me to be part of this thing.”

Said Brandon Crawford, “I didn’t know he competed, but it doesn’t surprise me.”

The Athletic spilled the (barbecued baked) beans Sunday night when it reported that Bumgarner admitted to his double life.

He had to after two reporters approached him at Diamondbacks camp and presented a photo of Bumgarner and another rodeo professional posing for a photo after they won $26,500 in a December team roping competition in Wickenburg, Ariz.

“Oh, boy,” Bumgarner told the Athletic when confronted with the photo. “This is ruining my alias.”

Everybody in the clubhouse knew that Bumgarner has dabbled in rodeo. He is a rancher and gave wife Ali a bull calf as a wedding present.

His brother-in-law is a professional rodeo competitor, and Bumgarner admitted in interviews some years back that he has tried it.

Bumgarner did not ever confess to competing professionally under a fake name.

Buster Posey was Bumgarner’s best friend and battery mate for 11 seasons and said he never heard of Mason Saunders. Mason is a diminution of Bumgarner’s first name. Saunders is Ali’s maiden name.

“I knew he was doing some roping,” Bochy said, “but I didn’t know he was doing anything on a competitive level. There’d have been no stopping him, though.”

Bochy knew Bumgarner was a daredevil. Everyone figured it out after the dirt-bike accident in April 2017 that dislocated the pitcher’s left shoulder. Bochy has other Bumgarner stories he is sworn not to tell, one involving a black bear.

“But this one tops them all,” Bochy said.

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Bumgarner competes in the team rope, where two horsemen lasso a steer. One snags his back feet, the other his head or horns. Neither has to jump off his horse and tie the legs like single-rider competitors do.

Bumgarner has said he ropes right-handed, leaving his precious pitching arm out of it (until he falls off the horse, of course).

Brandon Belt, who grew up in Texas, said he understands you have to use your right hand because of where the steer is when the horses are released.

Belt hasn’t done rodeo, but since he is a versatile master athlete he is sure he could make money like Bumgarner has.

“One hundred percent,” Belt said. “I seen it enough and watched enough on TV. I could do that.”

Now that Mason Saunders has been outed, the Diamondbacks face questions, like whether they knew “Mason” when they signed Bumgarner to a five-year, $85 million contract just days after he competed in a rodeo, according to the Athletic.

General manager Mike Hazen told a group of reporters Tuesday, “We are aware that Madison is a very strong horseman. We had conversations with him in the (negotiating) process. We know that he’s living on a ranch and does those things.”

Hazen would not comment on whether Bumgarner’s contract has any language that would cost him money if he were to be hurt riding.

When he fell off his dirt bike, the Giants could have docked him for the months he was out but chose not to. He was a World Series hero, after all, and they still had hopes of extending him.

One Giants official who requested anonymity so he could speak candidly said the club did not know of Bumgarner’s alter ego and had no reason to doubt that Bumgarner really fell off a dirt bike as opposed to being hurt riding a horse.

The issue for Arizona might be moot now that Mason Saunders is a household name.

“I have to think this is the end of him in competitive rodeo,” Bochy said.

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

Editor’s note: An earlier version of this story erroneously called the event calf roping.