Arguably the best team in baseball history wasn’t built around superstars. It was built instead around depth and consistency, and as the 2001 Mariners won 116 games during the regular season, they posted an 82 ERA- that was, therefore, 18% better than league-average. While the pitching staff wasn’t particularly noteworthy, it was healthy and solid and bolstered by an all-time-great defense, which made for an outstanding level of run prevention. The 2014 Mariners aren’t anywhere near a 116-win pace — that would be almost impossible, and in fact these Mariners have already lost eight more games than those other Mariners. But to date, these Mariners have posted an ERA- of 79.

Following the trade deadline, much of the talk concerns the rotations built in Detroit and Oakland. Both were strong before adding, respectively, David Price and Jon Lester, and those are the teams considered to have the most intimidating pitching staffs down the stretch. But it’s the Mariners who’ve had better run prevention than anybody else, by a decent margin, and two things are remarkable: it’s remarkable that that’s true, and it’s remarkable that the Mariners still aren’t presently in a playoff position.

To knock one thing out right away: it would be better to have RA-, but that’s not available on our leaderboards. And, honestly, it wouldn’t change very much; the Mariners have allowed just 28 unearned runs, fifth-fewest in baseball. So the ERA- isn’t deceptive, and while it’s somewhat insane what the Mariners have done, it’s extra insane what they’ve been doing lately. What comes next is going to feature an arbitrary endpoint, but this isn’t intended as analysis — this is just a summary of what’s certainly happened.

And what’s certainly happened is that, since the last day of May, the Mariners have played 59 games, or 36% of a full season. Over those 59 games, the Mariners as a team have allowed 159 runs, with a 2.50 ERA. Because I feel like you aren’t appreciating that, over more than a third of a full season, the Mariners as a team have posted a 2.50 ERA, that is a full run better than a 3.50 ERA, which would be a pretty good ERA. Clayton Kershaw has a career 2.52 ERA. For 59 games, basically, the Mariners have been preventing runs as if every game was nine innings of Clayton Kershaw.

Since that same date, the Mariners’ runs-allowed total is 46 runs better than the American League’s next-lowest runs-allowed total. The Mariners have allowed, over the span, fewer than half as many runs as the Rangers. And yet the Mariners’ record over the stretch is just fifth-best in the AL, behind the Orioles, A’s, Angels, and Royals. As the Mariners have had maybe the best run-prevention streak in franchise history, they’ve lost considerable ground in their own division. And this is because, since the last day of May, the Mariners are also tied for last in the AL in runs scored.

That more or less captures the essence of the team. But let’s step back now to look at the whole year, instead of just the last 2+ months. The Mariners’ team 79 ERA- is the best in baseball by five points. Since the mound was lowered before 1969, only six teams have finished with a lower ERA-, the 1993 Braves leading the way at 75. Since the same year, this Mariners rotation would rank in the upper 10%, but it’s the bullpen that’s been truly absurd — its 62 ERA- is topped only by the 2003 Dodger bullpen’s 61 ERA-. The Mariners projected to have a reasonably effective bullpen, but to this point it’s been almost unparalleled.

You can get yourself some of the way toward understanding how this has happened. Felix Hernandez is the AL’s Kershaw, and he’s been pitching at an even higher level than he used to. Hisashi Iwakuma also has a sub-3 ERA and xFIP. Chris Young, healthy now, has a history of beating his peripherals, and over his last ten starts he’s had four times as many strikeouts as walks. The bullpen has avoided both injuries and hits, and it’s been improved by the emergence of Brandon Maurer. Lloyd McClendon’s starters have generally taken him deep enough to afford bullpen flexibility, and it’s not surprising that any of those relievers have succeeded. In any given season, dozens if not hundreds of relievers will over-perform.

There’s also the matter of the team’s defense, which is why I’ve been careful to use the term “run prevention”. DRS thinks the Mariners have been average, but UZR thinks they’ve been considerably better, and Matthew Carruth’s team-level analysis is even more flattering. While the defensive unit lacks an Alex Gordon or an Andrelton Simmons, it’s also a unit that doesn’t have a glaring weakness (at least, anymore). The Mariners have all the elements to have an above-average run-prevention unit; throw in some good health and some good luck, and you’ve got a unit that right now is performing at a historic level.

Then comes the possible regression, which is the problem. Because the Mariners have had an extreme performance, you have to assume it’ll be closer to average going forward. At the moment there’s a 15-point gap between the Mariners’ ERA- and FIP-, and there’ve been just five bigger gaps since 1969. There’ve been no bigger gaps since 1991. The Mariners can’t really count on a 79 ERA- for the final six or seven weeks, which is why it’s imperative they start scoring runs. They can hope for continued good defense and they can hope for health and effectiveness out of James Paxton, but they should probably be closer to above-average than elite. The 2014 Mariners’ run prevention might be this year’s 2013 Cardinals hitting with runners in scoring position, or 2012 Orioles record in one-run games. That which is better than it ought to be could become what it ought to be at a moment’s notice.

But if it helps, the rest of the way the Mariners are projected for either the AL’s fifth-best record, or the AL’s third-best record. As one unit projects to do worse, the other unit projects to do better, with basically offsetting regressions. Adding Austin Jackson doesn’t hurt; getting Michael Saunders back should completely eliminate Endy Chavez. (The team’s been playing Endy Chavez.)

No matter where the Mariners go from here, there’s no disputing that, for two months and for four months, the run prevention has achieved at a level seldom before seen. Yet, these Mariners have won 52% of their games. The teams with the top 25 run-prevention units since 1969 have won an average of 60% of their games. So there exists the belief among some people that the Mariners are wasting the gift they’ve been given. That’s true in a way, as the Mariners are a non-elite team with an elite-level partial performance. But from the other perspective, the Mariners have taken full advantage of this run prevention, as a team with a lousy offense is a game back from making the playoffs. A team with so few runs allowed has little business being outside of the playoff picture; a team with so few runs scored has little business being anywhere close to the playoff picture. I think the only thing that really matters is that on August 7 the baseball still matters.