A month ago, I wrote that it was time to take the Pirates seriously, as their 33-20 record was a strong enough start to put them squarely in the playoff mix, even if we didn’t think they were going to keep playing like a .622 team going forward. Well, since that post was published, the Pirates have gone 18-10, which translates into a .642 winning percentage. Rather than beginning their regression to the mean, they’ve gotten better.

So, now, it’s July 1st and the Pittsburgh Pirates have the best record in baseball. They have a two game in the NL Central and a 10 game lead over the Washington Nationals for the second wild card. By pretty much any objective measure you want to use, it is now likely that the Pirates are going to make the postseason this year. At this point, wondering whether or not they’ll stay in contention is something of an outdated question; now, the real query now is just how good is this Pirates team?

Rather than starting with win-loss record to try to determine how much of that we should take seriously, let’s work our way from the bottom up instead. Here is the wOBA and wOBA allowed for every team in baseball, sorted by the difference between the two.

Team wOBA (Offense) wOBA (Defense) wOBA Differential Tigers 0.339 0.296 0.043 Cardinals 0.326 0.291 0.035 Braves 0.320 0.294 0.026 Red Sox 0.344 0.320 0.024 Athletics 0.320 0.298 0.022 Pirates 0.306 0.287 0.019 Rangers 0.321 0.302 0.019 Rays 0.325 0.307 0.018 Rockies 0.333 0.317 0.016 Reds 0.314 0.299 0.015 Angels 0.325 0.319 0.006 Orioles 0.334 0.329 0.005 Indians 0.329 0.325 0.004 Giants 0.312 0.309 0.003 Cubs 0.305 0.306 -0.001 Nationals 0.295 0.300 -0.005 Blue Jays 0.319 0.324 -0.005 Diamondbacks 0.311 0.318 -0.007 Dodgers 0.306 0.313 -0.007 Phillies 0.310 0.320 -0.010 Brewers 0.311 0.321 -0.010 Mariners 0.301 0.314 -0.013 Royals 0.301 0.315 -0.014 Padres 0.306 0.320 -0.014 Yankees 0.297 0.313 -0.016 White Sox 0.295 0.311 -0.016 Twins 0.313 0.334 -0.021 Mets 0.292 0.313 -0.021 Marlins 0.276 0.314 -0.038 Astros 0.295 0.351 -0.056

Despite being tied for 19th in offensive wOBA, the Pirates are 6th overall in wOBA differential because of their run prevention, which has been the very best in baseball. An average offense and elite run prevention might not be as well received as other paths to success, but there’s no question that it works if you can pull it off. There’s also no question that the Pirates overall win-loss record has gotten some help from sequencing, as a 19 point wOBA differential matches up closer to a 90 win team rather than a 100 win team.

Sequencing is mostly randomness, but it’s not entirely random. A team with an excellent and deep bullpen is more likely to outperform their expected win-loss record than a team with inferior relievers. There’s a reason the Chicago Cubs record doesn’t match their wOBA differential, and his name is Carlos Marmol. The Pirates bullpen, led by Jason Grilli and Mark Melancon, has been absurdly good this year, and here’s where that shows up:

I’ll let you guess which of those marks represents the Pirates’ run prevention in high leverage situations. And yes, that is the Dodgers on the far right, giving up a .360 wOBA when the game is in the balance. That Brandon League contract sure is working out well. The Pirates, for reference, are at .216; no other team is below .270. Between their three best relievers — Grilli, Melancon, and the unheralded Justin Wilson — they’ve faced 144 batters in high leverage situations and allowed opposing hitters to hit .135/.206/.194, good for a .183 wOBA. Those three have faced 39% of the total batters that have hit against the Pirates in critical situations, and they’ve been basically unhittable.

If you feel like we had this same story last year, you’re not wrong. The Baltimore Orioles bullpen basically carried them into the postseason last year, and even they weren’t as good at putting out fires as the Pirates relief trio has been this year. Last year, the Orioles relievers posted a +13.86 WPA, the highest mark of any relief group in baseball history. Through 81 games this year, the Pirates have a +7.42 WPA, which would prorate out to +14.84 over a full season. In other words, the Pirates bullpen has been more instrumental in winning games in the first half of 2013 than the Orioles bullpen was last year.

Of course, this is the kind of thing that isn’t all that predictive. The Orioles bullpen WPA is historically unique because relief pitcher performance is extremely volatile. After all, did anyone look at Jason Grilli, Mark Melancon, and Justin Wilson before the season started and say “hey, that’s an all-time great bullpen in the making”? The thing with surprisingly awesome performances is that they often end as suddenly as they started. The 2013 Baltimore Orioles bullpen has put up a +0.43 WPA. This is an unstable foundation to build upon.

But, also, the 2013 Baltimore Orioles are also still a good team, and still a playoff contender, even with their bullpen no longer dominating like they did a year ago. To counteract that regression, they simply turned Manny Machado and Chris Davis into superstars. It is too simple to look at a team’s performance based on great relief performances and predict that a crash is coming, because it ignores all of the players on the team that aren’t relievers, and their performances aren’t set it in stone either.

The Pirates bullpen is going to perform worse in the second half, if only because there’s no possible way for them to be any better. Regression is coming. But can the Pirates offset those losses by making up ground elsewhere, as the Orioles have done this year?

Well, it seems unlikely that anyone on their team is about to go all Chris Davis on the league, nor do they have any Manny Machados hanging out in Triple-A waiting for a promotion, but there are areas where this team can expect some improvement in the second half as well. The Pirates right fielders have hit just .227/.292/.366, so whether it is improvement from Travis Snider and Garrett Jones or a trade for a more competent outfielder, they should get a better performance from that spot on the field in the second half.

On Friday, Jeff noted that the Pirates pitchers have been historically terrible at hitting this yaer, posting the worst line of any group of pitchers in Major League history so far this season. Pitcher hitting doesn’t seem like the kind of thing that can make much of a difference, but in the NL, pitchers bat a couple hundred times in the course of half of a season. Going from a .092 wOBA to a .150 wOBA — roughly league average for pitcher hitting this year — doesn’t sound like it would be a big deal, but 58 points of wOBA over 175 PAs adds up to nearly nine extra runs, or almost one entire win in the current run environment.

There aren’t enough offsets here for the Pirates to keep this pace up, or even really keep up anything close to this pace. Our rest-of-season forecasts, which use the ZIPS/Steamer projection systems, still believe the Pirates are basically a .500 team over the rest of the season. Clay Davenport’s model gives almost the exact same result using different inputs, so it’s not just our projections being overly bearish. There’s a lot of room for regression in how the Pirates are currently winning games.

But at the same time, the rest of the season will not be played with the rosters as currently constructed. The Pirates .500 rest-of-season forecast does not include any July roster upgrades, and the Pirates have put themselves in prime position to make some additions to bolster their team for the stretch run. And perhaps most importantly, they’ve built a formidable cushion. Playing .500 ball the rest of the way would result in a 92-70 record, which would almost certainly be enough to capture one of the two wild card spots. And regardless of what the franchises record has been in recent second halves — seriously, any analysis that begins and ends by pointing to the second half record over the last two seasons is completely worthless — there is no objective reason to expect them to play worse than .500 over the rest of the year.

This Pirates team probably isn’t going to keep the Cardinals at bay, and they might even get passed by the Reds, who are a better team on paper as well. But, they’re a solid team that shouldn’t be expected to fall apart, and their roster construction could make them a very tough team to deal with in October.