Hey, why’s the area around second base at Citi Field so sparkly? Oh, it’s just some loose diamonds from Yoenis Cespedes’s necklace.

Cespedes blooped a double into right field in the first inning of the Mets’ 7-0 loss to the Braves and went charging hard into his slide at second. When he came up, half the stones in his necklace were gone, and he slammed the chain down on the ground in frustration.

New York shortstop Asdurbal Cabrera and umpire Bill Welke picked up some pieces between innings after the Mets stranded Cespedes to end the inning.

This is why, kids, you don’t wear anything to the ballpark you’re not okay losing. Stadiums are large places with lots of people where sometimes unimaginable things happen, like a foul ball flying right toward your face or a fielder swiping a tag that catches and shatters your diamond chain.

This happened last year, too, to Houston pitcher Lance McCullers. His black diamond chain malfunctioned in the middle of the American League Championship Series at Yankee Stadium. He spent a replay review digging through the dirt at the back of the mound to find the gems.

The “Official Baseball Rules” do not mention jewelry, and Major League Baseball does not otherwise restrict its usage. It’s common to see players wear chain necklaces or earrings for religious or stylistic reasons. The rule book merely prohibits glass or polished metal buttons that may reflect light into the eyes of fielders or officials.

Little League International and the National Federation of State High School Associations, high school sports’ national governing body, both prohibit players from wearing jewelry, aside from “medical appliances/devices [that] are considered to be jewelry.”

The NFHS wrote in a point of emphasis — a note to coaches, players and umpires — before the 2018 season that umpires will be cracking down on enforcing the jewelry ban during the season.

“Earrings and various other piercings can be problematic for a player if the piercing gets caught on equipment and torn away from the body,” the point of emphasis notes.

And, as Yoenis Cespedes learned the hard way, chains can break, too. That might hurt your neck and your wallet.

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