Rangers coach John Tortorella reportedly threw a plastic drinking bottle over the glass and into the stands during a confrontation with a fan on Friday night.
Washington defeated New York 4-0 in the game, but the Rangers still lead the series 3-2.
The incident took place in the third period.
"He was losing and he was frustrated, I guess," Capitals' season ticket-holder Claudette Chandonia said, according to a report in the Washington Post. "I couldn't believe it. I looked up, and he was throwing the water bottle -- and then it hit me right here, right in the head, and it bounced off me."
Report: Rangers' Tortorella Tosses Bottle At Fan