PITTSBURGH - Odubel Herrera is a confident man. The Phillies paid him $30.5 million last winter because they believed in their centerfielder's talent. The commitment extended deeper than that; the Phillies envisioned a player who could overcome the daily challenges this game presents.

But the last week was not a good one. Herrera batted 28 times. He registered 11 strikeouts and zero walks. He collected just four hits, three of which were singles. He entered Friday with an on-base percentage that had dipped below .300.

He has, at times, lacked composure. But confidence? Herrera said that will never be an issue.

"I know what I'm capable of. I'm mad at myself because I know that I can do better," Herrera said, through a team interpreter. "I know I'm capable of doing better things."

Herrera's problems at the plate are easily diagnosed: He has swung at far too many pitches out of the strike zone. He ranked sixth in baseball with a 41.5 percent swing rate on pitches out of the zone, according to Baseball Info Solutions data. The league average was 29 percent.

Herrera had swung at 34 percent of pitches out of the zone in each of the last two seasons. He has an innate skill for making contact, which allows him to sometimes expand the strike zone. That formula has not worked in recent weeks.

His swinging strike percentage has spiked in 2017 because he has picked the wrong pitches to attack. Teams have thrown him fewer fastballs than last season.

The Phillies have stressed this to Herrera, who is aware. Correcting it is another matter.

"He needs to be a little more disciplined in his pitch selection," Phillies manager Pete Mackanin said. "That's what he needs. You have to try to remind a guy what he did when he was successful."

Much of it is mental, Mackanin said, which is why Phillies hitting coach Matt Stairs has assumed the role of chief encourager.

"I swear to God I'm putting in the work," Herrera said. "It's frustrating because I think I'm doing what I'm supposed to do. When I'm at the plate I feel like I'm going to make good contact with the ball. But it's not really happening for me. I really don't know what's going on.

"I haven't been as disciplined as last year. I have to go back to that."

Herrera has not carried his offensive slump into the field, where various advanced metrics peg him as one of the game's best defenders in 2017. There has always been a disparity between how the metrics and scouts view Herrera's defense, but it has improved.

"What I think about is if I'm not hitting the ball, maybe I can make up for it by being a good defensive player," Herrera said. "Maybe I can take hits away from the other team."

Extra bases

Michael Saunders did not start Friday because of a sore groin, but he entered the game in the sixth inning when Daniel Nava, his replacement in right field, was injured. . . . The Phillies added Adam Morgan as an extra reliever to assist the taxed bullpen. He replaced Nick Pivetta on the active roster and could return to triple-A on Sunday, when Aaron Nola is activated.