Why this upstart team could crash the postseason party

Coming into 2023, you would have been hard-pressed to find many people who thought the D-backs had a realistic chance to reach the postseason. Their playoff odds on FanGraphs prior to Opening Day were just 15.3%. But if the season ended today, they’d be in the postseason for just the fourth time in 21 years.

Of course, the season doesn’t end today. There’s a lot of baseball left to be played. But that doesn’t mean we should write off Arizona. Here are five reasons the club could have staying power in this playoff race. (All stats are through Friday.)

1) They quietly have one of MLB's best rotation duos

Zac Gallen has cemented himself as one of the top pitchers in the game since the beginning of last season, ranking second among qualifying pitchers in ERA (2.66), third in FanGraphs WAR (7.0) and FIP (2.80), seventh in K/BB ratio (4.39) and 11th in innings (250 2/3).

The 27-year-old right-hander has taken his game to another level since the 2022 All-Star break, ranking first among qualifiers in ERA (2.12) and FIP (2.09) and producing 1.5 more fWAR than any other pitcher.

Most fWAR among pitchers since 2022 All-Star break:

1. Zac Gallen (AZ): 6.0
2. Spencer Strider (ATL): 4.5
3. Kevin Gausman (TOR): 4.4
4. Framber Valdez (HOU): 4.2
5. George Kirby (SEA): 3.9

Gallen threw 44 1/3 consecutive scoreless innings last August and September, producing the seventh-longest streak of the Live Ball Era (since 1920), then followed that up with another lengthy streak (28 innings) this April.

With a 2.97 ERA and an MLB-leading 2.10 FIP over his first 11 starts of 2023, he is on track to earn his first career All-Star selection (and potentially get the starting nod for the National League).

But he isn’t the only D-backs starter having an All-Star caliber campaign in 2023.

Through 10 starts, Merrill Kelly has posted personal bests in ERA (2.98) and strikeout rate (26%) while throwing 57 1/3 innings. Kelly also has the highest chase rate and whiff rate of his five-year career.

Kelly’s 3.67 FIP, 3.88 xFIP and 4.08 SIERA suggest he’s unlikely to carry a sub-3.00 ERA all season, but the 34-year-old has now pitched to a 3.28 ERA over 257 2/3 innings -- the eighth most in MLB -- since the beginning of 2022.

In that span, 19 pitchers across the Majors have thrown at least 200 innings and posted an ERA+ of 125 or better, per Stathead. The only teams with two such pitchers in that timeframe? The Astros with Framber Valdez and Cristian Javier and the D-backs with Gallen and Kelly.

Kelly's emergence as a viable No. 2 starter behind Gallen has been crucial considering how the rest of Arizona's rotation has performed. The six pitchers (including Madison Bumgarner, who was released) besides those two who have made a start for the D-backs in 2023 have combined to post a 6.19 ERA over 28 starts.

The hope for Arizona was that Brandon Pfaadt, who ranked 59th on MLB Pipeline’s Top 100 prospects list entering 2023, would step up. However, Pfaadt has allowed 22 runs over 23 2/3 innings in his first five starts and ranks in the 7th percentile or lower in a number of key Statcast metrics, including hard-hit rate (5th percentile), barrel rate (3rd percentile), chase rate (7th percentile), expected SLG (1st percentile) and expected wOBA (5th percentile).

2) Their rookie star is living up to the hype

Corbin Carroll burst onto the scene late last season, showing off his 80-grade wheels and producing an .830 OPS over 115 plate appearances. That was all the D-backs needed to see to sign their top prospect to an eight-year, $111 million extension in March.

By most meaningful metrics, Carroll has improved upon his abbreviated debut season:

• Average exit velocity: Up 4.0 mph
• Hard-hit rate: Up 8.2 points
• Barrel rate: Up 3.0 points
• Walk rate: Up 4.5 points
• Chase rate: Down 2.1 points
• Whiff rate: Down 7.9 points
• Strikeout rate: Down 7.2 points
• Expected SLG: Up .071
• Expected wOBA: Up .055

We knew the 22-year-old was going to run, but there was reason to question how much power he’d provide with his 5-foot-10, 165-pound frame. He’s erased any doubts with 21 extra-base hits (seven homers) and a .503 slugging percentage over his first 48 games in 2023.

On pace for 22 homers and 44 stolen bases, Carroll could become just the fourth player to reach the 20-homer and 40-steal plateaus in his rookie season, joining Tommie Agee (1966 White Sox), Mitchell Page (1977 A’s) and Mike Trout (2012 Angels).

3) They can run and field with the best of them

Defense and baserunning typically don’t get as much attention as hitting and pitching, but they can be important components for a winning team, too, and the D-backs are among MLB’s best in both categories.

After leading the Majors in Outs Above Average a year ago, the D-backs are tied for fourth this season. The club has capable defenders all over the diamond -- of the 13 players with at least 10 fielding attempts this season, nine have +1 OAA or better.

Arizona also ranks seventh in the Majors in BsR (3.4), FanGraphs’ all-encompassing baserunning metric that takes stolen bases, caught stealings and other baserunning plays (taking extra bases, getting thrown out on the bases) into account.

With Carroll leading the way, the D-backs are tied for sixth in stolen bases (42) and have one of MLB's highest success rates (84%) on steal attempts.

The Rays, Padres and Cubs are the only other teams that rank among MLB’s top 10 in both OAA and BsR.

4) Their offseason additions shored up their weak spots

Arizona had a relatively quiet offseason, but the moves it did make have all worked to make the team better.

The decision to trade outfielder Daulton Varsho to the Blue Jays for young catcher Gabriel Moreno and outfielder Lourdes Gurriel Jr. has been a home run for the D-backs.

After hitting only five homers over 121 games a year ago, Gurriel already has eight dingers to go with a .316/.369/.561 slash (152 OPS+) across 187 plate appearances.

And while Moreno hasn’t hit for much power, he’s posted a .302 batting average and a .735 OPS (102 OPS+) over 136 PAs. With the 23-year-old in the fold, the D-backs have gone from having the 20th-highest OPS among catchers in 2022 to the 10th highest in 2023.

The club also signed veteran third baseman Evan Longoria to a one-year deal, and while he only has a .729 OPS overall, he's produced an .866 OPS in 55 PAs against left-handed pitching.

Arizona was especially poor when facing left-handers last season, but they are much improved in that department this year, as Gurriel, Moreno and Longoria have combined for a .931 OPS over 168 PAs against southpaws.

The D-backs’ newcomers have helped the club go from ninth in the NL in runs scored per game (4.33) last season to third this year (5.08).

The back end of Arizona’s bullpen is also considerably better after the club signed Andrew Chafin and Miguel Castro. Chafin and Castro effectively replaced Mark Melancon and Ian Kennedy, who combined to post a 4.99 ERA with 79 K’s over 106 1/3 innings for the D-backs last season. In 2023, Chafin and Castro have combined for a 2.81 ERA, 49 strikeouts, 11 saves and 13 holds over 41 2/3 innings.

5) The NL is worse than expected

Perhaps the biggest reason why the D-backs seemed unlikely to make the postseason prior to Opening Day was that the NL looked to be absolutely stacked. The expectation was that the loser of the NL East battle between the Braves and Mets would grab one NL Wild Card spot and either the Dodgers or Padres would grab another, leaving only one playoff spot for the likes of the Phillies, Giants, Brewers, Cubs, D-backs and Marlins.

However, little in the NL has gone as anticipated.

The Padres, Cardinals and Phillies -- three of last year’s six NL playoff teams -- are under .500, and the Mets are just barely over the mark. The Giants and Marlins are also hovering around .500, while the Cubs are six games below it. And the Pirates are starting to fade after a surprising April.

Meanwhile, the D-backs were 16-13 at the end of April and have built on that in May, going 13-9. As a result, the upstart club has bumped its playoff odds north of 48% heading toward Memorial Day.