Last season was a concerning one for Jose Quintana. The consistent lefty came with lofty expectations to the Cubs in a trade for top prospect Eloy Jimenez in 2017, and largely lived up to them. However, 2018 was a different story. Quintana struggled with fastball command for a large part of the season, resulting in a career-high 9.2% walk rate. In combination with his lowest strikeout rate since 2015, this led to his lowest strikeout-minus-walk rate since his 2012 rookie season. His 14.7% home run per fly ball rate was a career high, despite the league home run rate taking a slight downtick from record highs last year.

Quintana also greatly struggled the third time through the order in 2018, allowing a .934 OPS compared to his career mark of .770. This makes sense, as Quintana was mostly a two-pitch pitcher, throwing mostly his fastball and curveball. Because neither was an especially dominant pitch, he struggled to be effective when hitters saw him the third time. He was also slightly worse against righties compared to lefties than he has been over his career so far.

In Quintana’s last three starts, though, he’s pitched the best he has in a Cubs uniform. Outside of an early relief appearance and a bad start against Milwaukee, he’s been outstanding this season. So what changed?

The main difference appears to be Quintana’s increased confidence in his changeup. As Sahadev Sharma writes at The Athletic:

In his first two outings, a four-inning relief appearance and a three-inning disastrous start in Milwaukee, Quintana combined to use his changeup just nine times (5.7 percent of the time). In his three starts since, he’s gone to it 35 times (11.5 percent) and gotten nine swings and misses, including three on the 13 he threw Tuesday night.

Using the changeup more and establishing it as a potential weapon should help to alleviate some of Quintana’s issues facing hitters a third time. It should also help him quiet right-handed bats a bit–Quintana is throwing his changeup to left-handed hitters only 0.1% more than last season (3.8)%, but against righties his changeup usage has gone from 7.6% to 12.3%. That’s not the only change he’s made to his pitch mix, however. Quintana has also been relying on his sinker more this year, especially against lefties–he didn’t throw a single four-seam fastball to a lefty in his most recent two starts.

While Quintana’s altered pitch usage is likely the predominant factor in his recent success, there are others that stand out as well.

Quintana has been throwing his pitches in the zone one percentage point higher than in 2018. On the first pitch of each at bat, hitters are swinging two percentage points less (Quintana’s lowest rate since at least 2015), but first pitch strike rate is up by nearly the same amount. This pattern of hitters being less aggressive and Quintana being more aggressive is demonstrated elsewhere, too. Quintana has the tenth lowest in-zone swing rate among qualified starters so far this season, meaning he’s getting a lot of called strikes (despite the lack of assistance from Cubs catchers). Why aren’t hitters swinging?

It’s most likely a combination of two things: 1) Quintana is hitting the edges of the zone a little more, and 2) batters are expecting him to be more wild because of his lack of command last year, so they’re being more patient. Quintana is also tunneling his pitches better than he has since 2013, according to Baseball Prospectus' pitch tunneling data, meaning hitters could be having greater difficulty distinguishing pitches that tend to be in the zone from pitches that often fall below the zone.

Not only are hitters not swinging at hittable pitches from Quintana as much, they’re also swinging and missing much more (nine percentage points) than they were last year, which would be the highest whiff rate of Quintana’s career.

So, Quintana is throwing more strikes, and hitters are swinging less in the zone and more outside the zone. Not only that, they’re making way less contact when they do swing outside the zone and slightly less contact on pitches in the zone. When hitters have made contact off of Quintana this season, they’ve been hitting the ball into the ground. Quintana is known as more of a fly-ball pitcher, but so far this season his fly-ball rate is way down from his Statcast-era high of 23.7% to 16.4%, while his ground-ball rate is up six points to 50.7%.

All these changes have combined for a great stretch of pitching. The results? Quintana has produced half as much fWAR (0.8) as last year (1.6) in about 16% of the innings. He’s on pace for 224 strikeouts in 174 innings, compared to 158 last year.

There could be an adjustment coming if hitters start being more aggressive with Quintana, or if his command wavers. For now, though, Cubs fans should enjoy the ride and hope Quintana continues to push Eloy Jimenez farther from their minds.