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Major League Baseball Commissioner Rob Manfred on Sunday defended the penalties imposed on the Houston Astros for a sign-stealing scheme during their World Series-winning 2017 season, saying the investigation could not have been conducted without giving players immunity.

The comments came a month after baseball authorities fined the Astros $5 million, stripped them of top draft picks for the next two seasons and suspended the team's manager and general manager, who were fired later.

But Astros players who had been granted immunity to participate in an investigation were not punished. Fans and players from other teams have criticized Manfred for not imposing harsher penalties.

Speaking to reporters at a spring training facility in Florida, Manfred said that in "a perfect world," in which investigators would have been able to gather the facts of the scheme without the players, they would have been disciplined.

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Two star players, second baseman José Altuve and third baseman Alex Bregman, offered brief apologies Thursday during a news conference.

Manfred said it was clear from the apologies that "they will live with questions" about the 2017 season "for the rest of their lives."

"Who relishes the idea of being a 2017 Houston Astro?" he said.

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Major League Baseball began investigating the scheme after the sports site The Athletic reported in November that the team illegally used a camera positioned in center field of its home stadium, Minute Maid Park.

The camera was used to help decode signals between catchers and pitchers on the visiting team, the site reported.

Manfred also responded to reports that players might strike back against the Astros by hitting batters with pitches, saying he had made it "extremely clear" that retaliation would not be tolerated.

"It is not helpful to the current situation," he said.