SAN FRANCISCO – Brandon Crawford is killing the Giants. And, yes, despite Crawford's leading role in Thursday's 3-2 loss to the Miami Marlins, it's harsh to put it that way.

It's antithetical to the baseball tradition of showing patience with a promising young player as he stumbles in his baby steps toward stardom. Yet it's no less true.

The 25-year-old Giants shortstop and fan heartthrob may become a star someday, but his youthful missteps – and those of other unproven Giants – are costing the team wins.

Crawford made a critical first-inning error, letting a grounder by Miami shortstop Jose Reyes go through his legs, to set up the Marlins' first run.

It was the 15th unearned run the Giants have allowed this season, far too many for a team that struggles to score.

Crawford's error loomed large all afternoon, and that unearned run was the difference in another gut-wrenching, one-run loss.

"I've never been through this before," Crawford said in the Giants' clubhouse, an unhappy space because they were swept in three games by the Marlins.

The Giants slipped below .500 to 12-13. And they will have to muddle through for up to six weeks without Pablo Sandoval, their best hitter and third baseman who broke his left hand and will have surgery today.

"I know I'm a good defender and it will come back. … Hopefully, I'll start to make the plays again," Crawford said.

The Giants are praying he will, too, because he's it – he's their shortstop. Only Starlin Castro of the Chicago Cubs has made more errors than Crawford at shortstop, though at least Castro is an offensive weapon.

Crawford is just about an automatic out. He's hitting .208, and only Clint Barmes of Pittsburgh has a lower on-base percentage among big-league shortstops.

"With young players, you're going to have your ups and downs," Giants manager Bruce Bochy said. "We have to stay behind these guys."

The Giants have no choice. They have to play the kids.

Veteran first baseman Aubrey Huff is on the disabled list with an anxiety disorder, Sandoval went down, and second baseman Freddy Sanchez is approaching the one-year anniversary of dislocating his right shoulder.

On Thursday, that meant Conor Gillaspie, 24, rushed from Fresno to play third in Sandoval's absence.

While Huff recuperates,Brandon Belt, 23, is the first baseman. Playing second Thursday was Joaquin Arias, 27, a solid defender who has never played a full season in the majors.

Then there was Crawford.

That's an entire infield of untested players learning their craft before sellout crowds on a team with championship aspirations.

That means Bochy is forced to make unpleasant choices, such as pinch hitting for Crawford in the seventh inning as the Giants mounted a serious threat. Crawford had made his second error of the game in the fourth inning.

The Giants were losing 2-1 by the seventh and were lucky to be that close. The Marlins had baserunners in every inning and left 15 stranded in all.

The Giants' only run at that point had come when left fielder Melky Cabrera grounded into a double play in the sixth inning, scoring right fielder Gregor Blanco from third.

Blanco went 3 for 3 on the day, and Cabrera brought him home a second time in the eighth inning for the Giants' other run.

But Bochy just couldn't trust Crawford in the seventh with two runners on and one out.

Of course, pinch hitter Nate Schierholtz, another unproven everyday player, popped out in Crawford's place – a terrible at-bat in an inning in which the Giants failed to score.

Brett Pill, another young player the Giants need, also made an eighth-inning out in a key spot, and Hector Sanchez, a young backup catcher, pinch hit in the ninth and grounded out meekly to end the game.

This after Sanchez had gone 0 for 5 the night before with three strikeouts.

Starter Ryan Vogelsong pitched seven innings, allowed only one earned run – and lost.

Bochy had the look of a guy who tosses and turns at night while pondering his young team.

"There is a fine line between wanting them to know you're behind them," Bochy said, "and at the same time not wanting them to bury themselves."

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