Through 59 games, the Oakland Athletics have been a juggernaut. Their 37-22 record is one game behind the Giants for the best record in baseball, and is the best in the American League by a game and a half over the Blue Jays. Where the A’s are really shining though, is their run differential. At this point in the season, the A’s have outscored their opponents by a total of 121 runs – more than both San Francisco and Toronto combined. To put that absurd number in perspective, only five teams had a better mark than Oakland’s +121 over the course of the entire season, and only the Cardinals were within 40 runs of Oakland’s mark on June 5th a year ago.
But what does a great run differential even guarantee a team? Run differential is generally thought of as a way to quantify future success by using past results. Thus at the end of the season, a team could have a great run differential and miss out on the playoffs because of shoddy luck over the course of the season. Similarly, a team could have a mediocre run differential and could sneak into the playoffs. We saw this situation happen in 2012, when the Orioles won the AL’s second wild card berth with a 93-69 record and a +7 run differential, which is more fitting of a .500 team. The Rays finished three games back of the Orioles with a 90-72 record, and a +120 run differential that was the second-best mark in baseball.
Generally, finishing with a better run differential guarantees that your team will have a better season, which seems obvious. The five teams with the best run differentials made the playoffs in the National League in 2013, and five of the top six in the AL made it, with the one non-qualifier (Texas) squaring off with the Rays in a one game playoff for the American League’s second wild card. A year earlier, the first season with the extra wild card, the pattern held true in the National League, but three AL teams that had a better run differential than the Orioles stayed home in October.
Is there a magic number with run differential? Well, just like with wins, we can’t guarantee anything. Generally, 90 wins puts a team in a good position for a playoff spot, but sometimes, the strength of the league forces the bar upward. One 90-win team has missed the playoffs in each year since 2010. Even with the introduction of the second wild card in 2012, at least one team with a run differential of +90 has missed the playoffs in 11 out of the last 12 seasons. Over that same 12 season span, just four teams with a run differential of +20 or worse (including two teams with a negative run differential) have made the playoffs. It’s much easier to outscore your opponents by more runs and fail to make the playoffs than it is to outscore your opponents by fewer runs (or not at all) and make the playoffs.
Playing in a top-heavy division can actually end up damaging some teams that finish with a high run differential. Last year when the Rangers missed the playoffs with their +91 differential, they finished 5.5 games behind the A’s, who had a +142 run differential. The 2012 Rays were in a division with the Yankees and their +136 differential, though the borderline miraculous Orioles and their unsustainable record in one-run games didn’t help. Looking back at the rest of our 12 season sample, all but three teams that finished with a +90 run differential or better and missed the playoffs were in a division with a team that had a better run differential than them For what it’s worth, all three of those teams (2003 Mariners, 2003 Astros, 2005 Indians) would have made the playoffs if the second wild card had been in effect at the time.
What have we learned today? Well, just like with a great record, a great run differential doesn’t guarantee anything. Teams hovering around the .500 mark have squirmed their way into the playoffs, just like teams hovering around a neutral run differential. And just like 90 win teams have been left out of the playoffs, teams with fantastic run differentials have been left out of the playoffs. Hell, those 2005 Indians that I mentioned earlier finished 93-69, and their +147 run differential was the best in the American League by 29 runs. They stayed home for the playoffs, because the White Sox won 99 games to win the AL Central and the Red Sox took home the AL Wild card with a 95 win season.
It obviously won’t hurt a team to outscore their opponents by as much as they can. But really, there are so many other factors at play. How often do you see a team win a three game series two games to one, but get outscored? The season usually balances out over time, but it’s wins and run differential isn’t a perfect correlation – that’s why we talk about expected, or Pythagorean, winning percentage so often when talking about differential.
As for the playoffs, we know they’re a crap shoot. The two best teams with the two best run differentials met in the World Series last year, but the last time the teams with the best run differentials met was in 2007, when the Red Sox and Rockies squared off (though the Rockies were half a game short of having the National League’s best record). Prior to that, it was 2004 with the Red Sox and Cardinals, despite Boston having the AL’s second best record. The 2002 Angels, 2007 Red Sox, and 2013 Red Sox are the only teams in our sample to finish with the best run differential in the majors and win the World Series.
The moral of the story is this: A’s fans, it’s still a long season. Your team has had an awesome two months, but even if they head into the Postseason with a record-breaking run differential, nothing is guaranteed. And while a weak-looking American League should help the A’s avoid the hard-luck fate of the 2005 Indians, there’s nothing that could stop the A’s from turning into a team like the either the Yankees or Phillies in 2011 in October, regular season juggernauts that bowed out quietly in the playoffs. Oakland’s great start should be praised, but even if they continue at this otherworldly pace, there’s no guarantee that their 25 season World Series drought will end.