Here’s the quickest way to understand what’s gone on in the field for the Oakland Athletics this season: Marcus Semien has arguably been their best defensive player. Yep. That’s the one. The same Marcus Semien who committed 35 errors as Oakland’s everyday shortstop last year. That’s not being totally fair to Semien, who has legitimately improved at short, but he’s still been average (at best) at shortstop, and in the field for the Oakland A’s this year, average at best is as good as it gets.

The numbers tell most of the story themselves. By team Defensive Runs Saved, the A’s rank last in baseball, at -44. More than 10 runs separate the A’s from the team in 29th place. By team Ultimate Zone Rating, the A’s rank last in baseball, at -30. More than 10 runs separate the A’s from the team in 29th place. We all know that these defensive metrics come with their error bars, but with this sort of gap, we can be pretty sure the A’s defense has been lousy. It’s not only hard to argue anyone’s been worse than Oakland in the field, it’s hard to argue anyone’s been close.

And it goes beyond just this year. Our defensive metrics go back to 2002. Since then, there have been 450 team-seasons, and Oakland’s UZR/150 currently sits 449th. In other words, at this rate, the 2005 Yankees might be the only team in the last 15 years with a worse defense than this Oakland club. Put DRS on a similar extrapolated scale, and the A’s take the “throne” from that same New York club.

The A’s are currently going at a historic pace, but we know the dangers of “pace,” and so we know it’s always better to use the projections. Unfortunately, the projections aren’t too kind either. Using our depth charts, we find that the A’s are projected to drop roughly another 11 defensive runs over the final two-thirds of the year — a vast upgrade over what’s happened so far, but certainly not good. Assuming the projections hold true and using a mix of DRS and UZR, the A’s would finish with something like -50 defensive runs saved. That’s a difference of roughly five wins on the schedule, and would rank as a bottom-25 team defense in the last decade-and-a-half.

So, at the current pace, they could be the worst ever. Even at a regressed, projected pace, they’re in the bottom 5%. This isn’t going to end well. I haven’t watched much Oakland baseball this year, so I can’t say for sure whether the eye test matches the numbers, but with the numbers being what they are, I can’t imagine it’s been pretty. And there hasn’t a bright spot on the field for Oakland. The futility is widespread:

Oakland Athletics Defensive Ranks Position Rank P 30 C 30 1B 25 2B 26 3B 30 SS 19 LF 20 CF 24 RF 15 IF 30 OF 23 Shifts 29 SOURCE: Baseball Info Solutions

They’ve got baseball’s worst infield defense, and a top-10 groundball rate. The Mets are able to hide their lackluster defense with a pitching staff full of strikeout machines; A’s pitchers have just a league-average strikeout rate. I don’t know what to make of the fact that those same pitchers have combined for a league-worst -11 DRS on their own. Could probably be interpreted as fluky, but then again pitchers are fielders, too.

To go to one more well, we can look to the Inside Edge data and see that it hasn’t just been the difficult plays Oakland’s had trouble converting (though they’ve had trouble there, too), but it’s been the routine ones that have killed them:

A’s Inside Edge Defensive Ranks Bucket Rank 1-10% 28 10-40% 19 40-60% 29 60-90% 30 90-100% 28 SOURCE: Inside Edge

Nowhere is a bright spot for Oakland, they’re not making the routine plays or the difficult ones, and in fact, things are even worse than they seem.

See, Stephen Vogt and Josh Phegley rank dead last in DRS, but DRS doesn’t include framing runs, and framing runs don’t help Oakland. Vogt has been a bottom-five framer, according to BaseballProspectus. Phegley has been in the negative himself. So, add that on top of what we’ve already uncovered about Oakland’s defense.

There’s not a simple fix to this. The A’s aren’t contenders this year, so the defense can be as bad as it wants to be for now, but for the A’s to turn themselves back into a contending club, the defense has got to turn itself back into a respectable one, and it’s not going to be easy. It’s the kind of thing that will require dedication and plenty of moving parts. At least Billy Beane isn’t against moving some parts around.

The Indians had a -40 defensive season in 2013 followed by a -70 season in 2014 before they pulled off one of the most remarkable defensive turnarounds we’ve ever seen. It all started with the swap of Asdrubal Cabrera for Francisco Lindor at shortstop. Calling up elite defensive catcher Roberto Perez from the minors, alongside slick-fielding third baseman Giovanny Urshela and utility man Jose Ramirez helped, too.

But, see, here’s the problem with Oakland. Their top prospect is Franklin Barreto, currently a shortsop, but here’s an excerpt from Christoper Crawford’s most recent scouting report: “…the fundamentals—or lack thereof—make his long-term position a question mark.” Barreto nearly matched Semien’s 35 major league errors at shortstop with 34 in the minors himself. Their next-best position player prospect is Matt Olson, likely future first baseman. Crawford: “…a lack of speed/athleticism makes his future as an unspectacular, though solid first baseman much more likely [than a corner outfielder].” Richie Martin, Matt Chapman and Yairo Munoz all project as big league defenders, but questionable big league bats.

Help in the way of everyday big league players with plus gloves at premium positions don’t appear to be on the way for Oakland as they were in Cleveland. Ideally, there would be obvious internal solutions to bump Vogt off catcher and Semien off shortstop as soon as next year for means of an immediate defensive improvement, but it’s not clear that’s the case. Oakland’s top prospects are defensive tweeners, just as their current major leaguers are the defensive tweeners who have contributed to baseball’s worst defense. Odds are, Oakland’s next contending team will look very little like the one that suits up now. A major overhaul is likely on the way, and defense ought to be a priority.