What's Eating Pablo López?

On one level, this is all pretty simple. Has Pablo López been good enough this season? There's a nuanced, layered, difficult, even self-contradictory answer, but there's also a pretty simple one: his ERA is 4.72. That's not good enough--not for a hurler the Twins needed to pitch like the ace he was down the stretch last season, and not as a highly-paid veteran on a team that cut back its payroll for 2024 and doesn't seem eager to raise it again for 2025 and beyond.

That doesn't mean López isn't a good pitcher. By no means does he seem to have totally lost his good stuff, and despite a couple of starts in which his fastball has been noticeably diminished, both he and manager Rocco Baldelli insist that he's healthy. He's struck out 27.9% of opposing batters, and walked just 4.0% of them. That's ace-caliber work, and his stuff remains ace-caliber, when he's commanding it. We can sum up the "yeah, but" pretty succinctly: he's giving up home runs at exactly the same rate at which he's issuing walks, and as a result, opponents are slugging .437 against him. Preventing home runs is the least stable of the three bedrock skills a pitcher can demonstrate, but when you struggle to do it, the other skills don't matter as much as one might like. López is giving up harder contact and getting fewer ground balls this year, and when hitters hit him hard, they're getting a lot of juice out of the squeeze.

Evaluating López is difficult, then, because he's winning as many at-bats as ever--as many pitches as ever. Sometimes, baseball is a game defined by probabilities. Win more matchups than the average pitcher (or batter, if that's your role), and you help the team win. This is why batting average was the first metric by which fans measured players for the first 70 or 80 years of professional baseball, and why on-base percentage is now recognized as the best individual indicator of a hitter's performance.

Now, however, we live in a somewhat different era. On-base percentage still matters a lot, and (flipping the image to read it from the pitcher's side) strikeout-to-walk ratio is still an excellent barometer of pitching ability. More than in the past, though, danger lurks throughout a big-league lineup, and runs are scored in sudden thunderclaps, rather than insistent showers of singles and runner advancements. The game is less about probabilities and more about payoffs than it used to be, which means that a vulnerability to the home run on the mound is more damaging and limiting than it used to be. López and the Twins are feeling that in a big way right now.

The gopheritis afflicting López lately is not a merely abstract concept, though, and we don't have to treat it as an inscrutable mystery. There are a couple of material problems at play. Let's identify them, so we can watch for signs of López fixing them in future starts.