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  • Writer's pictureBruin Sports Analytics

How the Arizona Diamondbacks Reached the World Series Against All Odds

By: Albert Carreno

Source: Axios

Since official playoff odds came into existence for major league baseball in 2014, there have been 160 teams that were given less than a 30% chance of making the playoffs before the start of the season. Out of these 160 teams, only 7 have defied the odds to make the playoffs, with only the 2015 Kansas City Royals shocking the world and winning the World Series. This year, we almost got to witness that same underdog magic from the Arizona Diamondbacks. A team that had lost 110 games in 2021 and 88 in 2022, there was little optimism surrounding the Diamondbacks entering the 2023 regular season. Question marks seemed to surround the entire roster: they were criticized for having little rotation depth beyond Zac Gallen, had an offense that lacked any notable stars, and an untrustworthy bullpen that posted the sixth worst ERA in the majors while blowing 27 saves throughout the year. With teams that were seen as more well rounded before the season such as the LA Dodgers, San Diego Padres, and San Francisco Giants, Arizona was given little chance to compete in the AL West. Their only way into the playoffs was considered to be through a wild card spot, but even achieving that feat seemed like a stretch. However, much to the surprise of many people, the Diamondbacks snuck into the playoffs, barely edging out several teams for the final wild card spot in the National League. Their regular season was far from impressive at 84-78, and considering the fact that their second half record was a measly 36-45, many people were justifiably doubtful of the Diamondbacks even winning a single playoff game. Still, rare occurrences do happen and the Diamondbacks proved this by going on a dominant playoff run. They swept the Brewers in the wild card round, swept the mighty Dodgers in the division series, and pulled off a seven game upset over the Philadelphia Phillies in the championship series, making it to the World Series for only the second time in franchise history. They ended up losing to the Texas Rangers in five games, but the sheer accomplishment of this team making the final round is something that will be remembered for a long time. Considering how the odds were stacked against them, it’s only natural for one to wonder: how did they pull off this playoff run? This article aims to provide an answer to that question through a thorough, statistical breakdown and comparison of the Diamondbacks’ regular season and playoff performances.

As previously mentioned, the Diamondbacks were far from a top team in the regular season. They had little business making the playoffs, but due to a much weaker and more wide open National League, they were able to slip in. Surface metrics hardly ever paint the complete picture when analyzing a team’s performance, but they can still provide a snapshot of a team’s abilities. Offensively, Arizona was about as mediocre as it gets as the graph below shows.

Their triple slash line, that is batting average/on base percentage/slugging percentage, was .250/.322/.408. These figures ranked 14th, 14th, and 17th in the MLB as seen above. Their team wOBA, or weighted on base average, was .317 and ranked 17th in the league. The Diamondbacks also only hit 166 home runs during the regular season, which came out to 22nd in the league. All these numbers are indicative of a team that wasn’t likely to dominate offensively, and considering they only scored 4.58 runs a game(14th in the league), that description seems to be accurate. One thought some people might initially have is that the Diamondbacks must have benefitted from greater offensive output in the playoffs. Maybe some of their players caught fire at the right time and the Diamondbacks were just able to rely on that to get to the World Series. But, as we see below, it’s rarely ever that simple. 

There seems to be hardly any difference between the Diamondbacks’s surface metrics in the regular season and in the playoffs. Their batting average and slugging percentage is slightly higher, but that’s about it from a performance standpoint. I will note though that I included BABIP, or batting average on balls in play. This metric is generally a decent barometer for luck(though it’s admittedly far from perfect) since it only considers balls in play that are not home runs. In the regular season, the Diamondbacks had a BABIP of .293, which is slightly below league average, but in the playoffs, they had a BABIP of .310. This mark is considered to be above average, meaning that Diamondbacks hitters likely did experience a bit more luck in the playoffs. It’s highly possible that on several occasions, certain balls put in play that are generally turned into outs were not. Arizona scored at a slightly higher clip in the playoffs as well at 4.82 runs per game, and this higher BABIP may also play a role in that. Overall, the Diamondbacks were mildly better offensively in the playoffs, but it still seems like too minor of a difference to consider it the game changer for them.

The other primary component of a baseball team of course is their pitching. Arizona’s pitchers in the regular season were about as mediocre as their hitters though. 

Their starting rotation and bullpen posted ERAs of 4.67 and 4.22, which as the graph shows, ranked 21st and 18th in the league, respectively. The underlying numbers behind these earned run averages suggest that these modest performances by Arizona pitchers were not due to bad luck either. The starters and bullpen both had FIPs (fielding independent pitching) over 4.35 and BABIPs right around the league average of .300; it’s even fairly reasonable to say Arizona relievers experienced a bit of luck as their collective BABIP was .285. Diamondbacks pitching also ranked average to below average in SIERA (skill interactive earned run average), WHIP (walks plus hits per inning pitched), and K/BB (strikeout-to-walk ratio). As previously mentioned, their pitching was never seen as a source of strength going into the season and their numbers this year proved why. Surprisingly though, once the playoffs began, Arizona’s pitchers were able to find ways to limit the run totals of opposing teams despite some of their underlying numbers seeming a bit off. The bar graph below supports this claim.

The graph shows a massive difference in ERA for the regular season and playoffs. However, this is strange because Arizona’s FIP and SIERA were fairly worse in the playoffs as opposed to the regular season(the higher ERA, FIP, and the SIERA are, the worse they are considered). FIP and SIERA are generally considered to be more accurate in regards to evaluating pitching performance simply because they are much more holistic; they take more factors into account with their formulas. When a pitcher experiences a large difference between these stats, it means they typically either had exceedingly good or bad luck. That said, these advanced metrics don’t mean much for the sake of this discussion; the Diamondbacks were clearly able to restrict opposing offenses much more effectively in the playoffs, and this better pitching performance was likely the primary catalyst for their unexpected run. Nevertheless, it’s only natural to be curious about how exactly they let up much fewer runs, and to satisfy our curiosity, we need to look deeper under the hood. 

In baseball, there are many factors to consider when determining what causes a team to have a lower earned run average. Some may claim strikeouts and walks matter most, while others might say ground ball percentage and hard hit rates contribute the most. However, the only way to find out what metric(s) are most significant in giving up fewer runs is through analysis. In order to do that, I took several metrics that are often mentioned in relation to run prevention and ran a random forest regression to see which of these metrics is considered to be the most correlated with lower runs against average. The results are depicted in the plot below.

As we can see, LOB% seems to far and away have the highest importance when it comes to earned runs against. It’s surprising how large of a gap there is in importance between LOB% and BB%, the second most important variable considered, but there may be an explanation for LOB% being so important. The fact of the matter is that no matter how good a team’s pitching and defense is, they will give up baserunners. As a result, the opposing team will normally have at least some opportunities to score throughout the game. It is under these situations that quality pitching is most important to limit the amount of runs a team allows. Logically, it makes sense that if a team gives up more home runs with runners on base than home runs with no runners on base, for instance, they will give up more runs overall solely because their pitchers were unable to leave those runners on base. For teams to win games, it’s these big moments with multiple runners on base when their pitchers need to deliver. The linear model below illustrates this point.

This linear regression model strongly validates the above statement, showing a strong positive correlation between a team’s total wins and their pitchers’ LOB%. It has an R-squared value of 0.54.

These observations are also largely corroborated by the Diamondbacks’s postseason success. Their LOB% improved by over 6% in the playoffs, and they allowed about 1.25 less runs per game. Looking at the Diamondbacks’ game logs during the playoffs this year, we can see that there were a lot of close games. 9 out of their 17 playoff games, to be precise, were decided by three runs or fewer. Stranding a few extra baserunners really makes a significant difference in these tight affairs and can ultimately determine who wins the game. It’s evident Arizona’s pitching kept its composure in these high stress scenarios, but one also has to give credit to their infield defense. Over the course of the postseason, they turned a whopping 58 double plays, which is over 20 more than any other team. Without these standout pitching and defensive performances with runners on base, it’s doubtful Arizona makes it all the way to the World Series.

Unfortunately though, the Diamondbacks were not able to seal the deal and win their second World Series in franchise history. It was a closely contested series, even though the Texas Rangers would end up defeating them in five games. Arizona lost two games they could have just as easily won that ended up being the difference. They lost the first game 6-5 despite carrying a lead into the final inning and they lost the third game 3-1 thanks to a 3 run third inning by the Rangers. Other than that one inning, the Diamondbacks pitched really well and deserved a win. But as we mentioned before, a team’s ability to keep opposing offenses at bay with runners on base is critical, and in this five game series, Arizona’s LOB% was only 69%, or 8% lower than what it was in their first 12 games of the playoffs. Their offense also largely dried up outside of a 9-1 game 2 victory, which does not make for a great combination. That said, it would be not truthful to say the Rangers humiliated the Diamondbacks, but it would be truthful to say they were the better team and made big plays and got big outs when it mattered most. Still, Arizona’s unexpected postseason run will be one to remember for a long time and goes to show the value of a team standing their ground in dangerous situations and finding a way through them.



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