German Marquez is on quite the run. In the second half of the season, Marquez’s 2.3 WAR ranks third in all of baseball among pitchers behind only those marks recorded by Jacob deGrom and Patrick Corbin. His 2.29 FIP and 2.79 ERA since the All-Star break are both fantastic. He’s struck out nearly one-third of the batters he’s faced with five times as many strikeouts as walks. He’s doing all of this while pitching his home games in Colorado, and he’s just 23 years old. That’s quite the dramatic turnaround for a pitcher who put up a 4.73 FIP and a 5.53 ERA in his first 16 starts of the 2018 season. Like many young pitchers with a boatload of talent, Marquez has spent his first few years in the big leagues experimenting with different pitches and usage patterns. He seems to have found one that works.

A year ago, Marquez was primarily a fastball-curveball pitcher. He would mix in a change every now and again, and he did experiment with a slider, but it wasn’t used often and it stayed up in the zone. With a mid-90s fastball and good curve, Marquez produced a 21% strikeout rate, 7% walk rate, and an ERA and FIP in the mid-fours. In Coors Field, those still represented above-average numbers. For Marquez to progress, however, he was going to need to develop a third pitch. When Eric Longenhagen discussed Marquez ahead of the 2017 season, he anticipated the introduction of that third pitch.

Marquez also has a plus curveball in the 76-81 mph range that has a slurvy shape to it but bites hard and has solid depth. A back-foot curveball is the best weapon Marquez has against left-handed pitching right now, as his changeup is still below average. But Marquez is just 21 and his delivery is loose and fluid so there’s likely more coming from the changeup. Marquez’s command elicits similarly bullish projection because of the delivery and athleticism and he’s already throwing plenty of strikes. He’s a relatively low-risk mid-rotation arm, an above-average major-league starter.

Longenhagen mentioned the change as a potential addition, and Marquez did work to make that change more of a weapon heading into this season. That plan hasn’t exactly worked out. Marquez is throwing the changeup under 10% of the time this season. Even against lefties, he’s turned to it on just 11% of all occasions. What’s improved most for Marquez is the slider, and it is fooling hitters. Here’s Nick Hundley swinging at a slider despite holding a 2-1 advantage in the count:

The pitch works well in and out of the zone. When he throws the slider outside the zone, Marquez induces swings around 40% of the time, and batters swing and miss on two-thirds of those attempts. When the pitch is in the zone and batters swing, they make contact roughly 80% of the time, but on 44% of sliders in the zone, the hitter doesn’t bother to swing, like Evan Longoria in this 0-2 count.

Nor has the improvement of the slider hurt the effectiveness of the curve, either. The curve is really good. Take a look at it.

Marquez has recorded an 18% whiff rate on his curve this year and allowed just a 35 wRC+ on curves ending a plate appearance. Of his 183 strikeouts this season, 91 have ended with that pitch. The curve, though, was also really good last season, producing a 16% whiff rate and a 34 wRC+ on pitches ending a plate appearance. Of his 146 Ks last year, 84 came by way of the curve. The slider is new, and he’s been using it more as the season has gone on. The graph below documents a five-game rolling usage rate showing Marquez’s four-seam fastball and slider.

German Marquez Increased Slider Usage vs. RHB Pitch First Half Second Half Change FA 46.6% 38.6% -8.0% SL 24.4% 30.2% 5.8% CU 19.6% 22.4% 2.8% SI 7.0% 7.7% 0.7% CH 2.4% 1.1% -1.3%

Marquez upped his slider a bit more in June, but a steadily growing commitment to the pitch beginning at the end of July — along with diminished use of the fastball — is what corresponds to his great streak. The increased slider usage at the expense of the fastball has been uniform against both lefties and righties. Here’s righties by half.

Here’s lefties:

German Marquez Increased Slider Usage vs. LHB Pitch First Half Second Half Change FA 53.1% 46.2% -6.9% CU 20.7% 20.0% -0.7% CH 11.3% 11.6% 0.3% SI 7.8% 8.6% 0.8% SL 7.0% 13.0% 6.0%

Against lefties, the slider was the least used pitch in the first half, and it has jumped up to third. Remarkably, he’s improved against lefties, but he’s actually improved more against righties in the second half by completely dominating them.

German Marquez By Half Batter Hand First-Half K% Second-Half K% First-Half BB% Second-Half BB% vs. RHB 30.2% 40.2% 7.9% 4.7% vs. LHB 18.1% 23.5% 8.4% 7.8%

The increased use of the slider alone isn’t enough to make Marquez better. He’s also improved at getting strike one. The graph below shows rolling first-strike percentage along with contact percentage this season.

German Marquez and Strike One Count K% BB% FIP Through 0-1 34.2 5.2 2.52 Through 1-0 23.2 13.2 4.16

Getting ahead in the count is important for all pitchers, including Marquez, as the table below shows for the Rockies’ righty.

Marquez has always avoided walks, but pitching coach Steve Foster has worked with the 23-year-old to be more consistent with his delivery to avoid giving away pitches and getting more command, as this Patrick Saunders piece indicates. The efforts seem to have paid off. Here’s a graph showing all of the release points on pitches from 2017.

Now here’s the same graph from this season.

Marquez’s release points are condensed in a much tighter area this season. It’s possible that curveball will always come out of the hand differently than the fastball. Perhaps one advantage of the slider is that it gives Marquez an offspeed pitch where he can maintain the same look to a batter. Marquez was solid last season as a mostly two-pitch starter. He struggled the first month of the season with walks, and as his slider usage grew and his command got better, the strikeouts went up as the walks went down. He’s only given up four home runs in the second half, and even if that number might rise a bit, Marquez will still be very successful.

With the emergence of Kyle Freeland and the continued success of Jon Gray, the Rockies have a very good 1-2-3 in their rotation right now. The only other teams in baseball with at least three pitchers who’ve recorded three or more wins this year are Cleveland (with four), Houston, and the Mets, with the Rockies trio containing three of the four pitchers under 27 years old. The Rockies tried to duplicate their success last season in the bullpen with expensive signings. That didn’t work, but the Rockies are succeeding anyway this season with a trio of good, young pitchers. German Marquez might be the best of the bunch.