Not every rookie will leave his mark on baseball like Aaron Judge and Cody Bellinger did a year ago, but each club has a prospect or prospects who should crack its big league roster in 2018. Below are MLB Pipeline's choices for the rookies who will make the biggest impact on each team in the National League West.
• Impact prospects: NL East | NL Central | NL West | AL East | AL Central | AL West
Arizona: Taylor Clarke, RHP (No. 7 on D-backs' Top 30)
Opening Day 2018: Triple-A Reno
The D-backs might get help in the bullpen from arms like Jimmie Sherfy or Jared Miller, but if a spot in the rotation needs to be filled, Clarke could be the one to step in. While he doesn't have eye-popping stuff, he does have a four-pitch mix that he knows how to use well, something he's shown in climbing the ladder and being among the organizational leaders in ERA, strikeouts and wins two years in a row.
Colorado: Ryan McMahon, 1B/2B/3B (No. 2 on Rockies' Top 30; No. 41 on Top 100)
Opening Day 2018: Rockies
While Colorado's decision to re-sign Carlos Gonzalez may push Ian Desmond to first base and obstruct McMahon's path to an everyday role, the rookie might be the best hitter of that trio. After encountering adversity for the first time with a down year in Double-A in 2016, he fixed his left-handed swing and finished second in the Minors in hitting (.355/.403/.583). McMahon should hit for both average and power and also is capable of backing up third base (his natural position, albeit one where he's blocked by Nolan Arenado) and second base. A 2013 second-rounder who played quarterback as a California high schooler, he could be the next Rockies passer-turned-slugger, a tradition that includes Todd Helton and Matthew Holliday.

Los Angeles: Walker Buehler, RHP (No. 1 on Dodgers' Top 30; No. 12 on Top 100)
Opening Day 2018: Triple-A Oklahoma City
Buehler had Tommy John surgery shortly after signing as a 2015 first-rounder from Vanderbilt, then pitched just five pro innings in 2016. Fully recovered last season, he rocketed from high Class A in April to Los Angeles in September, showing better stuff than he had before his elbow was reconstructed: a 95-100 mph fastball, along with more powerful versions of his curveball and slider. Once he learns to harness his improved arsenal, he eventually should settle in as the Dodgers' No. 2 starter behind Clayton Kershaw, though he'll open 2018 in Triple-A. So will talented outfielder Alex Verdugo, who's also ready but similarly blocked by veterans for now.

San Diego: Franchy Cordero, OF (No. 10 on Padres' Top 30)
Opening Day 2018: Disabled list (groin injury)
That Cordero led the Minors with 18 triples while also tallying 17 home runs and 21 doubles last season speaks to his athleticism and tools as well as his overall capacity to make things happen at the plate. He followed that by garnering MVP honors this offseason in the Dominican Winter League, and then slashed .343/.465/.714 in 43 plate appearances in the Cactus League before suffering a groin injury that will sideline him at the outset of 2018.
San Francisco: Steven Duggar, OF (No. 3 on Giants' Top 30)
Opening Day 2018: TBD, S.F. or Triple-A Sacramento
Club officials acknowledge that Duggar is their center fielder of the future, and that future could come as early as Opening Day because he has outperformed his veteran competition during Cactus League play. He had some of the best all-around tools among college position players in the 2015 Draft, yet lasted until the sixth round because they didn't always translate into production at Clemson -- something that hasn't been an issue in pro ball. He now demonstrates solid or better ability across the board with the exception of his merely decent power, and he's well suited to cover ground at spacious AT&T Park.