It starts with a thud sometimes.

A “thwack.”

A baseball gets away from a left-handed pitcher and it runs in on the hands of a left-handed hitter, and maybe on Feb. 24 the reflexes aren’t as sharp as they’ll be on July 24, or even March 24, and so instead of glancing off the meaty part of the forearm, ball hits bone.

Ball breaks bone.

“Sometimes you look at a guy get hit and you immediately think to yourself, ‘Well that’s broken,’ and it winds up to be nothing,” Yankees general manager Brian Cashman said late yesterday afternoon. “And sometimes you think, ‘That’s no big deal,’ and …”

He smiled a forced, painful smile.

“That,” he said, “is baseball.”

And so Curtis Granderson goes away for 10 weeks, his right forearm fractured by a J.A. Happ fastball, and the Yankees’ spring gets even more interesting by suppertime than it was at breakfast.

Already Derek Jeter had taken some swings in the batting cage and some ground balls at shortstop and declared he’d be ready to play in a real game by March 10. Already Phil Hughes had left the premises to go soak in a pool trying to soothe his balky back. Already Cashman had fielded his daily quota of Alex Rodriguez questions, reaffirming that he expects A-Rod back by the All-Star break.

“His rehab is going well,” Cashman said, and he was in a playful mood when he said it, around 11 in the morning, chiding a small corps of reporters for trying to continually make the A-Rod story bigger than it is, as if that’s even physically possible.

By 4 in the afternoon, the playfulness was gone, he was serious as a tax audit, and looked like a man yearning to answer questions about the media making the A-Rod story bigger than it is, or about his third baseman’s heart belonging to Boston, or about the looming experiment playing Granderson in left and Brett Gardner in center that was sure to fill a few notebooks in the coming weeks.