Keira Knightley's Broadway Debut Was Interrupted by a Screaming Fan

There will be added security going forward.

Knightley, 30, is currently appearing in "Therese Raquin."

“Roundabout takes the safety of their actors and audiences very seriously and extra security will be added beginning tonight," the company that operates Studio 54, where the show is playing, said in a statement. "For obvious reasons, we cannot comment on the exact nature of the additional security measures.”

During last night's performance, a man in the audience rose from his seat in the mezzanine, stood at the railing and starting shouting, a source told ABC News.

When Knightley did not respond, the man yelled, “Five seconds is too long to wait for a response!" according to the source.

The man has not been arrested and was taken to a hospital for mental evaluation, a police source told ABC News.