Depth has never been more important in the game than it is now, and the ability to fill in for an injured player or pick up the slack for a struggling one are key components for any successful team.
Some players are more easily replaceable -- even for short periods of time -- than others, and this week, we take a look at who the most indispensable player is on each team. In some cases, it's the team's best player, but not always.
D-backs: Paul Goldschmidt
The D-backs didn't need a reminder of how important Goldschmidt was to the lineup, but they got one in May. The six-time All-Star had a miserable month and was hitting just .198 by May 22. It was no coincidence that Arizona lost 15 of 17 at one point during May and finished the month with an 7-19 record. Goldschmidt provides not just outstanding offense but is also a three-time Gold Glove Award winner. There is no obvious alternative at first base with the D-backs sometimes using Daniel Descalso there when Goldschmidt gets a rare day off.

Dodgers: Kenley Jansen
Jansen is not only the most indispensable player on this team, but maybe any team. In the Dodgers' first five losses after he went on the disabled list with an irregular heartbeat, four of the games were lost in the last inning. Even though Jansen hasn't been as dominating as in previous years, he has still been so good that he made his third All-Star team. Current management realizes his value. Despite the fact that they don't believe in handing out huge free-agent contracts, the biggest one they have signed is Jansen's five-year, $80 million deal.

Giants: Buster Posey
The six-time All-Star catcher influences the club's fortunes almost daily. Though his hip problems have muted Posey's offensive numbers, he remains the one Giant who opponents tend to skirt in tight situations. He manipulates the bat extremely well, making him the ideal man to have at the plate under any circumstance. Defensively, Posey remains an expert receiver who's skilled in the art of pitch framing. More importantly, he commands the trust of San Francisco's pitchers, who have been bright spots for the team. And Posey's ability to play first base gives manager Bruce Bochy some flexibility in assembling each day's lineup.

Padres: William Myers
The Padres' lineup is just different when it's anchored by Myers. They've learned the hard way this year as he has spent three stints on the disabled list. When Myers is healthy, he is a force, and his upside on offense rates higher than anyone else on the team, even Eric Hosmer. Myers' newfound versatility has become key for San Diego. He can play across the outfield, and now he's added third base to his repertoire. That's allowed the Padres to give opportunities to a handful of youngsters based on matchups.

Rockies: Trevor Story
The Rockies have strong starting pitching and stars all over the diamond, such as third baseman Nolan Arenado, right fielder Carlos Gonzalez, center fielder Charlie Blackmon and second baseman DJ LeMahieu. But it's tough to come up with a workable Plan B if something were to happen to Story. Former top pick Brendan Rodgers is currently on Triple-A Albuquerque's disabled list with a left hamstring injury -- plus he's 22 and still learning. Story's power can help transform the lineup, and his work helps support a pitching staff that is driving Colorado's push for the postseason.