CHICAGO -- As hard as this might be to believe, the Cubs have a secret weapon on their side as they head toward the postseason. 
It's John Lackey. Specifically, Lackey's slider.
We know a lot about Lackey's competitiveness, but not so much about the pitches in his toolkit. He's known more for challenging hitters than his finesse, but you don't pitch almost 2,700 innings without having a few tricks up your sleeve.
Lackey arrived in Chicago speaking about the chance to add to the World Series rings he earned on the 2002 Angels and the '13 Red Sox, and he famously said after a start on Aug. 4 that he didn't come to town "for a haircut.'' He opened the season as the Cubs' No. 3 starter behind Jake Arrieta and Jon Lester, and he has pitched almost exactly as Theo Epstein had envisioned he would.
Lackey will take a 9-8 record and a 3.42 ERA into a start against the Reds on Wednesday night at Wrigley Field. He spent time on the disabled list in late August with what was called a strained shoulder, but he has dispelled concern about his health, ramping up to seven innings the last time out.
With Kyle Hendricks leading the National League in ERA and Lester joining him on the NL Cy Young Award short list, it's easy to take Lackey for granted. But as he stokes his emotions for the "big-boy games'' the Cubs will play in October, he's very quietly gone 2-1 with a 2.36 ERA in his past seven starts.

During this stretch, Lackey has held opponents to a .198 batting average. The key has been a slider he generally throws 83-84 mph at the bottom of the strike zone or below.
Cubs manager Joe Maddon says the slider is essentially the same pitch he saw when Lackey was a rookie with the 2002 Angels, but the numbers tell a different story. They say that Lackey's slider -- always good, but in recent years, not considered among the elite breaking pitches in the Majors -- has become one of the best pitches in baseball.
It falls off the table with late action, accounting for five of Lackey's eight strikeouts against the Brewers last Friday. About one out of every four pitches he's thrown this season has been a slider.
Opponents swing and miss 41 percent of the time, with only about one out of every eight balls put in play against the slider resulting in a hit (.129 opponents' batting average). This could be revealed as a difference-making weapon in October, especially with it being commanded by the pitcher with the most postseason experience (20 starts, 127 1/3 innings) among active players.

Perhaps because the 37-year-old Lackey has had three starts in which he gave up six or seven earned runs (including two in April), the emergence of his slider has been largely unreported. Lackey wasn't one of the Cubs' seven All-Stars. He's been able to bide his time, waiting for the October opportunity that brought him to Chicago.
According to FanGraphs' metric valuation of pitch values, the Cubs have pitchers who rank No. 1 in the effectiveness of three of the five basic pitches:
• Hendricks' changeup generates a weighted score of 20.3, putting it ahead of the changeups thrown by David Price (16.6), Jeremy Hellickson (11.8), Rick Porcello (11.1) and Marco Estrada (10.2).
• Arrieta's fastball generates a weighted score of 30.5, putting it ahead of the fastballs belonging to José Quintana (27.8), J.A. Happ (26.5), Max Scherzer (25.2) and Ian Kennedy (22.2). (Side note: Arrieta has not pitched as well as in his NL Cy Young Award-winning season of 2015, but metrics show that's due to some regression in his hybrid cutter-slider and other pitches, not the velocity or movement of his fastball.)
• Lackey's slider generates a weighted score of 25.5, putting it ahead of the sliders of José Fernández (22.8), Kenta Maeda (19.7), Chris Archer (17.4) and Tom Koehler (16.4).
Last season, Lackey's slider was ranked in the middle of the pack by FanGraphs. It was his fastball that was moving the needle, and that dynamic has been turned on its head in 2016, although Maddon says the slider is behaving the same as always.
"It's more of a slurve than a slider or curve,'' Maddon said. "It's a slurvy pitch. I think it looks almost exactly like it looked back in the day.''
While Maddon hasn't tipped his hand, Lackey is widely expected to pitch behind Lester, Arrieta and Hendricks in the postseason. But he's currently lined up to be the No. 2 starter, and he just might stay there.
Either way, don't be shocked if Lackey winds up playing a big role. He's got the track record as well as an old pitch that has never been nastier.