Phillies pitcher Jesús Luzardo knows what’s happening to cause his struggles. The thing he doesn’t know yet is why.

At times this season, Jesús Luzardo has looked like two different pitchers.

There’s the version of the Phillies left-hander with a sweeper that can get opposing hitters twirling in the batter’s box. But there also has been another version, one who allows run after run because he can’t find the zone at all or he’s in the zone too much.

On Wednesday against the Red Sox, Luzardo was both versions at once. He took a no-hitter into the fifth inning, but things unraveled immediately after the Red Sox advanced a runner to second base for the first time.

» READ MORE: Phillies’ five-run lead slips away as Red Sox prevent a sweep in extras: ‘That fifth inning was just a killer’

Masataka Yoshida led off the fifth inning with a double, and then Luzardo completely lost the strike zone. He issued four walks — missing badly — to force in two runs, and capped it by serving up a grand slam to Romy González.

“It’s unacceptable,” Luzardo said. “Four walks just can’t happen in the whole game, and shouldn’t happen in one inning.”

Luzardo knows what’s happening. The thing he doesn’t know yet is why or how to stop it.

“Out of the windup, clearly, isn’t the problem,” he said. “It’s when we get in the stretch. So I feel like other teams know that. Just back to the drawing board, in terms of that.”

Luzardo has faced 51 batters in July with the bases empty and has faced 32 batters with runners on base. According to FanGraphs, he has a walk rate of 5.9% with the bases empty and pitching out of the windup. But as soon as a batter reaches base and he starts pitching out of the stretch, that walk rate skyrockets to 25%.

And when he’s not walking batters, he’s being hit hard. Opposing hitters have a .375 batting average against Luzardo with men on base in July but are hitting .188 with the bases empty.

Fielding independent pitching measures a pitcher’s effectiveness on outcomes solely in their control: strikeouts, walks, hit batters, and home runs. The league average was 4.09 entering Thursday.

Luzardo’s FIP out of the windup this month is 2.02. Out of the stretch, it’s 9.45.

This is a new problem. His career splits are fairly even: a 8.8% walk rate with runners on, 8.2% without.

Luzardo said he’s working with pitching coaches Caleb Cotham and Mark Lowy to try to get to the bottom of the issue. He had previously theorized that his struggles had stemmed from a change to his hand placement in the stretch earlier this season. That adjustment was made after the Phillies believed Luzardo had been tipping his pitches.

“We’re still grinding through it,” manager Rob Thomson said. “When you think you’ve got something fixed, it might be something different. You don’t know.”

Now, Luzardo has gone back to the hand placement he had earlier in the season.

“The setup in the hands is the same. You break it down mechanically, you watch the video, everything’s the exact same,” Luzardo said. “So whether it’s teams breaking it down and finding something. … It’s just a matter of going back and having confidence that those pitches are going to be made.”

One thing Luzardo does know: it’s not a physical issue.

“My stuff is the best it’s been my whole career,” he said. “So it’s not a stuff problem. It’s more of command, making the right pitch at the right times, executing the pitches. Whether it’s me understanding that I’m not right now, right out of the stretch, I just need to get it right.”

In the postseason, a team only needs four starting pitchers at most. At certain points this year, it was easy to imagine Luzardo’s sweeper translating to an elite asset in a Phillies postseason bullpen. But that would be tough to pull off if he can’t be trusted with runners on base.

That possibility, of course, only matters if they get that far. Right now, solving the issue becomes more urgent every time Luzardo walks out to the mound. Opposing teams know that all they need to do to cause the lefty to spiral out of control is get a man on base.

“There’s no excuses,” Luzardo said. “It needs to happen now.”