Tonight, the Pirates will unveil their biggest pitching acquisition of the millenium when Chris Archer takes the mound against the St. Louis Cardinals. He has been the prize of the trade market the last three seasons, so it’s ok to pinch yourself when you see him warming up to Wiz Khalifa’s “Black and Yellow” around 7:05 p.m.. It is a move that is so anti-Pirates that nobody expected it. That includes Archer, who purposely tried to stay in the dark when it became trade rumor season.

”I didn’t know how interested the Pirates were in me until I heard in [GM] Neal’s [Huntington] voice the passion, the joy, the excitement that was there to have me on board,” Archer said in his introductory press conference.

While most of Pittsburgh is excited as Huntington, there are a few doubters out there. While Archer has ace stuff, it has not translated to ace-like results the last three seasons. Over the last two calendar years, he has a 3.99 ERA and a 1.26 WHIP. In the same time frame, Ivan Nova has a 4.01 ERA and a 1.25 WHIP. The skeptics do have a case for some cautious optimism.

So can Archer be an ace in Pittsburgh, or at the very least be a difference maker in the homestretch of the season? Let’s take a look.

Archer started slow in April, posting a 6.61 ERA and 1.59 WHIP while allowing six home runs in 32.2 innings. In that first month, opposing batters had a .377 wOBA, and lefty batters had a 1.076 OPS.

Archer did not worry too much in that first month, though.

”That’s baseball. We play 162 games and make 33, 34 starts for a reason,” Archer said. “...Ever since the end of April, I’ve pitched like myself.”

Since May 1, Archer has a 3.13 ERA, 3.20 FIP, 1.28 WHIP and is averaging 3.3 strikeouts per walk. Batters have a .300 wOBA since then, and lefties have been held to a .602 OPS.

One key difference between April Archer and the rest of the season is his arm slot. His release point had been fairly consistent month to month over the previous three seasons, but in April, his horizontal release point dipped about six inches.

It’s roughly back to where it has been now, so this may have been a problem the Rays and Archer have already fixed.

Speaking of going to back to old habits, Archer experimented with his foot placement on the rubber earlier this year. He traditionally stood on the left side of the rubber, but in the early parts of this season, he moved a step towards third base, as documented by Jason Collette of The Process Report.

But Archer is now back on the left side. This and the arm slot may have been an experiment gone awry, but now his delivery is back to normal.

Archer also seems to have found his changeup again and is using it effectively against lefties. In March and April, he threw 57 changeups to southpaws, resulting in a .284 batter wOBA and a 24.6% whiff/called strike rate. In the 108 changeups he’s thrown since May, one-third have been a whiff or called strike and batters have a .183 wOBA.

Archer has done a much better job catching the low, outside corner since May.

But the changeup and delivery have not been the core of Archer’s problems this year. That would be the effectiveness of his slider.

From 2015-2017, Archer’s weighted slider value was 60.8 runs above average, according to Fangraphs’ pitch values. In that time span, the only pitches that were more valuable were Corey Kluber’s curveball (77.1 weighted runs), Jake Arrieta’s fastball (65.9) and Max Scherzer’s slider (61.1). Going by this metric (and even the eye test), it was probably a top five pitch in baseball.

This year, it has been worth 0.1 weighted runs above average. It is downright pedestrian. And just like how his changeup has been better because of pitch location, Archer’s slider hasn’t been effective because he’s hanging it more. Here are the pitch heatmaps of his slider locations from 2015 (top) and 2018 (bottom):

He has allowed 51 hits on sliders this year, with the majority of them being in the heart of the plate.

He’s catching middle-middle far too often and isn’t burying the pitch. It still has good spin and whiff rates, but the mistake pitches are being hit. He’s also throwing it a ton compared to other Pirates starters (42.7%, roughly as often as he throws his fastball). For how fastball oriented the Pirates make their pitchers be, it will be interesting to see how often they let him throw his breaking stuff.

So even though he is having trouble locating his best pitch, Archer has looked good after he was done experimenting in April. If he can start burying that slider again, he could be the Bona Fide ace the Pirates have needed for decades. If not, he still looks like a major upgrade to the rotation.