However, Nunez saw the ball clearly from his vantage point at third base. As Posey stared helplessly skyward, Nunez raced toward home plate. He took a small leap as he caught the ball on the edge of the grass on the first-base side behind home plate, just in front of the warning track.
"Some plays, you don't even think about it. They just happen," Nunez said.
Giants manager Bruce Bochy couldn't remember having seen a remotely similar play during his lifetime in professional baseball.
"He's so athletic and he's so fast," Bochy marveled. "I knew that he had Buster covered. You could see that he could see that Buster didn't see the ball. That's just good hustle and good game awareness."
Nunez actually ran around Posey, who inadvertently was blocking his path to the ball.
"I was halfway trying to guard my face in case the ball fell on top of me," Posey jokingly said.
Despite this human obstacle, Statcast™ calculated Nunez's route efficiency was 97.8 percent, enabling him to cover 111 feet while reaching a top speed of 18.5 mph during his pursuit.
Nunez's momentum carried him across the dirt before he used the backstop and the netting to halt himself, ending up in a seated position in front of the entertained fans perched at field level.
At once amazed and appreciative, Posey and left-hander Madison Bumgarner saluted Nunez by fist-bumping him as he returned to his position.
Chris Haft has covered the Giants since 2005, and for MLB.com since 2007. Follow him on Twitter at @sfgiantsbeat and listen to his podcast. This story was not subject to the approval of Major League Baseball or its clubs.