Jordy Mercer is the new starting shortstop for the Pittsburgh Pirates. Clint Barmes is now a moving part, an accomplished glove man on call at multiple infield positions. The shift will have an impact on both sides of the ball.

From an offensive standpoint, the changing of the guard makes perfect sense. The 35-year-old Barmes is a .246/.294/.383 hitter in 1,040 big-league games and has been trending in the wrong direction. The 27-year-old Mercer has less of a track record — just 145 games — but has hit a solid .273/.325/.425.

Mercer will supply more bang for the Bucs, but he won’t replicate Barmes in the field. The 6-foot-3 Mercer isn’t a defensive liability, but he came up through the system as an offense-first shortstop who dabbled at second base and at third base. The player he’s replacing is a pitcher’s best friend.

“Clint Barmes is one of the best defensive players in baseball,” Scott Spratt, of Baseball Info Solutions, said. “Since 2010, only Brendan Ryan (73) and Andrelton Simmons (60) have more Defensive Runs Saved at shortstop than Barmes’ 50. He has tremendous range and has been an above-average contributor on balls to his left (+28 plays), straight on (+23 plays) and to his right (+8 plays).

“Jordy Mercer is still a bit of an unknown,” Spratt added. “He falls just short of 700 career MLB innings at shortstop, where we estimate he has cost the Pirates one run with his defense. With the caveat that the small sample could have an impact on this, Mercer’s biggest weakness appears to be his throwing arm. He has made eight bad-throw Defensive Misplays and Errors (DMEs) in his limited innings. That is approximately one bad throw per 87 innings at the position, which is the sixth-worst rate of the 51 shortstops who have 500 or more innings since 2012. Barmes has just 13 bad throw DMEs over that time in nearly 2,000 innings, which is one per 151 innings.”

Mercer merits a chance to show those numbers can be thrown out the window. He knows he’s not Barmes, but he’s not short on confidence. When I caught up to him in spring training, he fielded questions about his defense ability with self-assured honesty.

“I’m happy with my defense,” Mercer told me. “I’ve always considered it one of my strong suits. I’m not worried about that at all. Everybody is going to say, ‘He needs to improve, he needs to improve.’ Well, of course I need to improve. But I’m not going to stress about it. I’m going to do my job and continue to try to get better.”

Mercer has a good mentor. He also has the luxury of playing for a team that will optimize his opportunities to make plays.

“I’ve worked with Clint ever since I’ve been up here,” said Mercer, who debuted with the Pirates in 2012. “He’s taught me about different angles on balls, how to position guys, reads off the bat, pretty much everything. A lot goes into being at the right spot at the right time, and that‘s something he‘s really good at.

“Positioning is huge,” he added. “A batter will hit a ball where it might normally be a base hit, and you‘re right there. Instead of it being something you maybe can’t get to, you moved over a few steps and made the play.”

Mercer’s comment on positioning is especially pertinent. The number of balls he and Barmes get to aren’t solely a product of their individual skills. SABR president Vince Gennaro addressed the subject in a more general sense at last month’s SABR Analytics Conference: Does having better data on positioning reduce the premium we put on a fielder’s range and increase the premium we put on sure-handedness? In the opinion of ESPN’s Jon Sciambi, the answer is probably yes. Sciambi pointed to the Pirates infield as an example, saying last year’s team had three guys with average to below-average range — Barmes being the exception — yet played plus defense.

Barmes is on board with his team‘s probability-driven approach to defense, but cautions that data points only go so far.

“It’s safe to say positioning is what gives you range,” Barmes told me in Bradenton. “Putting yourself within a step or two of where the ball is going to be hit is the goal. It’s the key to making as many plays as possible.

“We have the percentages on each hitter and will position accordingly. But as the game goes on, things can change. Maybe the pitcher doesn’t have his command and is missing his spots. When guys are missing toward the heart of the plate, professional hitters are going to hit holes a lot easier. That makes it more difficult for us, as infielders, to know where to be on certain pitches.”

Jeff Locke knows the value of experience. He also has full confidence in Mercer.

“Barmes is so educated at playing his position,” the Pirates left-hander said. “He’s played a lot of games there, so his anticipation is really good. But Jordy isn’t much different. He’s just a younger version.”

I asked Locke to elaborate on the similarities between Barmes and Mercer.

“I can’t really say how they play individually, but I can collectively,” Locke said. “They’re both going to give us great defense every time out. Last year Jordy spent a lot of time mirroring, and learning from, Barmes.”

After pausing for a moment, the lefty continued.

“One thing I love about Barmes is that he’s not one of those guys where if there’s a slow runner it’s ‘pump, pump, I’ve got time.’ He likes to get the ball and get rid of it. I played with Jordy throughout the minor leagues and he’s not really any different. We don’t have much flash on this team. You’re not going to see glove flips and behind-the-back tosses. Our guys get the ball and make the out.”

I asked the two shortstops how their styles compare.

“There are some similarities, but there are some differences as well,” Mercer said. “The similarities are the way we take angles and how we position ourselves. The difference is — and he’ll tell you this, too — is that he’s an unorthodox fielder. I’m a more-traditional fielder.”

Barmes agreed: “I’ve heard the word ‘unorthodox’ a lot. I could probably sit here all day and come up with things I do a little differently as far as technique goes. Over the years, I’ve become comfortable doing things in a way a lot of guys may not teach.”

I asked Barmes for examples.

“More than anything, it’s probably my footwork and how I set up on a routine ground ball,” he said. “For most guys, the left foot is half a step in front of the right when they go down to field the ball. That ties me up, so I go the opposite. I like my right foot to be maybe half a step in front of my left foot. It frees up everything and I can watch the ball into my glove better. If it takes a hop, I’m able to react a little quicker.

“Another thing that’s helped my career is the backhand. That’s something I’ve worked with Jordy on. Instead of worrying about trying to get around balls — fighting to get myself in that position — when in doubt I’ll go to my backhand, The more I worked on it, the more confident I got. Then it became throwing on the run, putting my body in a good position to make a strong throw on a ball that’s going away from first base. But as for comparing Jordy and me, he has his footwork and way of throwing the ball, and I have mine.”

Clint Hurdle’s assessment of the two?

“They spent the entire season together last year and it’s been a work-in-progress — a learning-in-progress — for Jordy,” Hurdle told me. “Barmes has been there to offer advice, and Jordy has learned a lot by watching Clint play. But the skill sets are similar — the ability to throw on the run, the ability to backhand the ball across the body, the throws. Probably the biggest thing Barmes has helped Jordy with is establishing good angles and routes to ground balls. I’d say Jordy has a similar skill set on the defensive side of the ball than Barmes.”

Would the Pirates manager place Mercer on the same tier of defensive excellence as Barmes?

“No, it’s going to take time,” Hurdle said. “He has to get games under his belt and make plays.”

Barring the unforeseen, Mercer is going to get a lot of games under his belt on a team with World Series aspirations. There’s a high likelihood he’ll out-hit his predecessor — perhaps by a meaningful margin — but Pirates pitchers are used to elite defense in the middle of the diamond. How much Mercer contributes with his glove may go a long way in determining whether Pittsburgh returns to the postseason.