A unit of Activision Blizzard Inc. has punished a player for expressing support for Hong Kong's protest movement, the latest example of a U.S. company attempting to rein in speech that might displease the Chinese Communist Party.

Blizzard Entertainment said it was banning Ng Wai Chung, also known as Blitzchung, from its professional Hearthstone esports competition for a year. Blizzard is also withholding money he had already earned in the company's top-tier Grandmasters tournament, which Ng said in a Twitter message cost him $10,000 of prize earnings. The move was triggered when Ng — dressed in a gas mask and goggles in defiance of authorities' ban on face masks — used a slogan in support of Hong Kong's pro-democracy protesters during a post-match interview.

"After an investigation, we are taking the necessary actions to prevent similar incidents from happening in the future," Blizzard said in a statement. On Chinese microblogging site Weibo, the official account of Hearthstone reposted Blizzard's statement in Chinese. "We will, as always, resolutely safeguard the country's dignity," it added.