The Houston Astros’ sign-stealing scandal not only devalued their championship in 2017—it also raised serious doubts about the legitimacy of the stellar performances of all of their batters.

For years, the Astros’ lineup practically broke baseball, hitting a ton of home runs without the barrage of strikeouts that almost always accompanies that kind of power. It defied all logic, until details emerged of the Astros’ scheme to bang on a trash can to relay catchers’ signals in real time and provided a simple explanation: The Astros succeeded at the plate because they knew what was coming.

But now it’s 2021, and plenty of new safeguards are in place around the league to prevent that sort of cheating from happening again. General manager Jeff Luhnow is gone. Manager A.J. Hinch, bench coach Alex Cora and many of the players from the offending Astros squad are gone, too. 

And yet the Astros are winning again, in almost exactly the same way they did in 2017.

The Astros are once again challenging for the best record in the American League and are serious World Series contenders, even with ace pitcher Justin Verlander missing the entire season because of an elbow injury. 

They entered Sunday leading the majors in batting average and ranked second in OPS. They are also the only team in the sport that strikes out in less than 20% of their plate appearances, closing in on their fifth straight season with the lowest or second-lowest strikeout rate in the major leagues.

Meanwhile, the Astros also make contact on more than 80% of their swings, a MLB high. The difference between the Astros and the second-best team in contact rate is greater than the difference between the second-best and the 27th-best. The top two players in the AL in batting average both play for the Astros, outfielder Michael Brantley and first baseman Yuli Gurriel.

Alex Bregman, center, and manager Dusty Baker Jr. greet Michael Brantley as he returns to the dugout.

Photo: Adam Glanzman/Getty Images

James Click, the general manager who replaced Luhnow after he was fired last year for his role in the scandal, recognizes how this all looks. “I’m fully cognizant of the fact that if you say that, I’m sure somebody will say, ‘Well, they must be up to something.’” 

And yet the fact remains: The Astros still seem dominant—even without the assistance of a garbage can.

“How people use our performance in 2021 to inform their opinions about years prior to that I think is up to them,” Click said.

There were reasons to wonder how the Astros would fare heading into the season. They faltered during the pandemic-shortened 2020 campaign, going 29-31 and finishing under .500 for the first time since 2014. Shortstop Carlos Correa hit .264 with a .709 OPS, below league average. Third baseman Alex Bregman hit .242. Second baseman José Altuve, the American League MVP in 2017, struggled worst of all, putting up a dismal .219 batting average in 48 games.

Then October came, and suddenly everything changed. Benefiting from an expanded playoff format that increased the number of participants from 10 to 16, the Astros sneaked in with the No. 6 seed in the AL and immediately took off. They swept the Minnesota Twins and beat up on the Oakland Athletics before falling to the Tampa Bay Rays in Game 7 of the championship series, one victory away from the pennant. Correa and Altuve combined to hit .368 with 11 homers in the postseason, a sudden return to form.

“It was very difficult to know which was the real team,” Click said. 

The Astros have provided an answer, thriving in a hostile environment every time they leave the confines of Houston. They played last season with nobody in attendance, avoiding the wrath of every opposing fan base that viewed them as the ultimate villains. Crowds are back now, and as a result the Astros have been on a summer-long tour filled with boos, jeers and taunts.

That was especially true earlier this month, when the Astros made their long-awaited return to Los Angeles to take on the Dodgers, the team they beat in the World Series in 2017. More than 52,000 fans packed into Dodger Stadium—the most of the season at any ballpark in the majors at the time—on two consecutive nights for the sole purpose of voicing their displeasure with the Astros. Fans brought inflatable trash cans. Just about every Astros foul ball was flung back onto the field. At least one person dressed up as Oscar the Grouch from “Sesame Street,” a character who famously lives in a trash can. 

Dodger fans hold signs during a game against the Houston Astros.

Photo: Carmen Mandato/Getty Images

Click compared the environment to playoff games. It felt like a potential World Series preview, and the Astros appeared to relish it. Lance McCullers Jr., who started one of the games on the mound, called it “probably the most fun I’ve had pitching in quite a long time.” Dusty Baker, the Astros’ 72-year-old manager, said, “This is a game I would have enjoyed playing in.”

“If you’re not willing to withstand the criticism you’re going to get in every stadium we walk into, if you can’t handle it, it’s tough,” second-year reliever Blake Taylor told reporters recently. “It takes something special to wear the Astros across your chest.”

Being hated certainly hasn’t fazed the Astros. Their records at home and on the road are both strong, in spite of constantly being booed and screamed at every time they walk onto a field that isn’t at Minute Maid Park. If anything, they appear to be embracing their role. So while Click stopped short of saying that the Astros are feeding off the criticism, he acknowledged that the team “is performing very well in those environments and in those big moments.”

They’re doing it in the same way the Astros always have: by mixing power with contact to create an offensive formula no other team in the majors has been able to replicate for years. Once the sign-stealing scandal became public, it seemed as if the Astros’ success at the plate was too good to be true. Maybe it wasn’t—even if the stench of suspicion might never fade away.

“That’s something that we just have to take head on in this organization,” Click said. “But that’s behind us.”

Write to Jared Diamond at jared.diamond@wsj.com