How Pablo Lopez Got Back to Bullying Hitters and Being the Twins' Superb Stopper

There’s a credible argument that, in some measure, Pablo López’s rough first half was not fully deserved. Through the All-Star break in mid-July, he had pitched to a disappointing 5.11 ERA over 104 innings. That really wasn't a fair reflection of the skill or value of a pitcher who had struck out 27.9% and walked just 5.3% of the batters he’d faced. The 22.6-point delta between López’s strikeouts and walks, usually one of the best predictors of future run prevention, was the 8th-best among 68 qualified pitchers at the time. Yet, his ERA was 65th among that same group.

The most straightforward explanation for that disconnect is that López allowed 18 home runs in the first half, tied for 4th-most on the list. His rate of 1.6 home runs allowed per nine innings in the first half was well above his 1.1 per nine career norm, pushed up by the league’s second-highest home runs-per-fly ball rate (15.8%). The issue with long balls was compounded by poor sequencing luck — he stranded only 65.5% of the baserunners he allowed to reach, about 8 points below his norm, and the 5th-lowest rate on the aforementioned list. 

López’s fielding independent pitching (FIP) estimate at that point was a solid enough 3.84, and the 1.26-run gap between his actual ERA and his FIP was MLB’s 2nd-largest.

It was clear he wasn’t pitching as poorly as his top-line numbers indicated, but it was also clear that he was not pitching as well as he did last year, when he ascended to the top of the Twins’ rotation.

Misfortune had a role, but López was also getting hit harder, more often. His exit velocity allowed, hard-hit rate, barrel rate, and expected production on contact numbers had all trended the wrong way compared to last season. His sweeper, a key to last season’s rise, and his always highly regarded changeup were both returning negative results. Something needed to change. 

Now, through August, López has thrown three scoreless outings in a row (part of a 20 2/3-inning scoreless streak), which have punctuated a run of great work since the All-Star break. He’s worked to a 1.92 ERA over 51 2/3 innings in the 2nd half, which has whittled his seasonal mark down to 4.05. More importantly, he’s again suppressing hard contact and keeping the ball in the yard.

Something has changed. Let’s dive in on what.

Things Tend to Even Out
Let’s start with the easy ones that don’t require much #analysis. López’s batted-ball and sequencing luck have turned in his favor. In the second half, his batting average allowed on balls in play (BABIP) is down about 35 points, to .268, and he’s stranded 87.3% of the runners he’s allowed. Just 9.3% of his fly balls have carried over the fence. The early season misfortune has swung the other way.

López’s slugging percentage allowed is about 80 points lower in the second half, which is certainly aided by giving up fewer homers, but also by giving up lower-quality contact to opposing hitters. His opponents' average exit velocity is more in line with last season, down to 86.6 mph from 88.2 mph, and almost half of that contact has been on the ground (up from just under 40% in the first half), where extra bases are hard to come by.

What’s changed to enable that?