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7/19/2014 11:39 P.M. ET

Alvarez works extra time on his throws

PITTSBURGH -- Early Saturday afternoon, Pedro Alvarez took ground ball after ground ball at third base. Being watched by a few coaches, the attention wasn't on his glove, but what he did after he had the ball.

Alvarez committed his 20th throwing error of the season Friday night, which led to a run that nearly cost the Pirates. It was the third baseman's 21st error of the season -- six more than anyone in the Majors -- and was his third errant throw in his last four games.

The defensive gaffes are nothing new for Alvarez, who has led the Majors in errors both of the last two seasons with 27, a mark he's on pace to break sooner than later in 2014. But what's different this year is that Alvarez's arm is getting the best of him.

From a glove standpoint, Alvarez has had his best season at the hot corner, picking grounders, making barehanded plays and committing just one fielding error. For reference, 26 of his 54 errors (48.1 percent) in the past two seasons were non-throwing mistakes.

Pirates manager Clint Hurdle, who has used a defensive replacement for Alvarez late in games seven times in July, said most of Alvarez's off-target throws happen on similar types of plays -- when Alvarez fields a grounder and has extra time to set himself before tossing across the diamond.

"He's trying to do everything he can to improve mechanics," Hurdle said. "More often than not, it's a setup when he throws. It was one particular play more often than not that presented him with some challenges. …This guy has probably played a more athletic third base this year, defensively, than any other year that he's been here. The challenge has been on the throwing side, and more or less, been on one particular play."

Hurdle has been known to give a player a few days off if he's slumping at the plate, but that may also translate to when someone is in a defensive funk. Alvarez was in the Pirates lineup Saturday in the second of a three-game series against the Rockies. But the Pirates are in the midst of a string of games against multiple left-handers -- Alvarez is .188/.268/.281 against southpaws this season.

"Sometimes I think a blow could help any player, backing away," Hurdle said. "We've also talked about taking time off from work, because [Alvarez] is a creature that loves to work and loves to try to do things to get better. We'll see how that plays out, especially with the large volume of left-handers that come in early."

Beaning keeps Marte out of lineup, from pinch-hitting

PITTSBURGH -- Starling Marte was held out of the Pirates' starting lineup Saturday and didn't play against the Rockies, a day after being hit in the helmet by a 93 mph fastball.

Marte initially stayed in Friday night's 4-2 victory and was evaluated on the field after taking an Adam Ottavino heater to the head. He was removed from the game two innings later, as Travis Snider took over Marte's post in left field -- which manager Clint Hurdle called a precautionary move.

Hurdle thought Marte could possibly be available for Saturday night's game off the bench, but said after a 3-2 walk-off win that the team decided it was best if the 25-year-old took the night off completely.

"Right at game time, the decision was to give him another night," Hurdle said. "Keep him from all activity tonight, and we'll see where he is [Sunday]."

Marte is hitting .258/.329/.390 in 84 games this season with 26 extra-base hits and 34 RBIs.

First number, last word

29: As in the age Pirates reliever Ernesto Frieri turned on Saturday. The right-hander, who also wears No. 29, has allowed six runs in seven appearances (four innings/13.50 ERA) since joining the Pirates in a trade three weeks ago.

"I think there was a point in time around second base that he just made his mind up that he was going to go. There was never a point where he saw [third-base coach Nick Leyva]. Now that comes with baseball awareness; that comes with experience. That's one area he has plenty of room to improve upon." -- Clint Hurdle on Starling Marte trying to stretch a triple into an inside-the-park home run on Friday.

Worth noting

• Pirates prospect Adrian Sampson came within two outs of a no-hitter for Double-A Altoona on Friday night. Sampson, who is ranked as the Bucs' 19th-best prospect by MLB.com, had the no-no broken up in the ninth inning by Bowie's Mike Yastrzemski (Carl's grandson). Sampson took the shutout instead, and has a 2.58 ERA in 20 starts for Altoona.

Stephen Pianovich is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.