NBC said in a statement that it had complained to Twitter about the posting of Mr. Zenkel’s e-mail address. “According to Twitter, this is a violation of their privacy policy,” the network said. “Twitter alone levies discipline.”

A Twitter spokeswoman said the company did not comment on individual users for privacy reasons.

In the case involving the comments about Mr. Daley, the authorities said they were questioning a 17-year-old boy in Weymouth, England, under a 1988 law that outlaws “the offense of sending letters etc. with intent to cause distress or anxiety.”

The move came after the teenager wrote on Twitter, “you let your dad down i hope you know that,” following Mr. Daley’s failure to win a medal in one of the diving events. Mr. Daley’s father, Robert, died last year of brain cancer.

“I worry that this will become the norm,” wrote Padraig Reidy, news editor of Index on Censorship, a free-speech group, in a blog entry. “Man says nasty thing on the Internet, nice people get upset by nasty thing, nice people demand something be done about nasty thing, police pursue easy conviction (all the evidence is online after all, and there are a million willing witnesses), nasty man gets convicted and everybody slaps each other on the back for having done their bit. The thrill of active netizenship.”

The police action was surprising because it came only days after an appeals court overturned the conviction of a Briton in a similar case involving Twitter, in which the man had jokingly threatened to blow up an airport after his flight had been delayed by a snowstorm. A lower court had convicted him of sending a menacing message, but the appeals court rejected that.

Before the Olympics, most of the attention on social media related to the Games had focused on marketing issues, after Britain passed a special law to protect Olympic sponsors from so-called ambush marketing.

Several American track and field athletes who are sponsored by Nike, which is not a sponsor, have taken to Twitter to criticize the restrictions.

Christine Haughney contributed reporting.