To interfere with someone's role, as in a performance, by interfering with their scripted or intended speech.
The person who introduced me stepped on my lines by giving a long summary, including all the good anecdotes.
1986, Carol Addison Takacs, Enjoy Your Gifted Child, page 51:
... interrupting often takes place when someone else in the group is telling a joke and the bright youngster blurts out the punch line — not because he has heard the joke before but because he sees what is coming and finds it funny. And so, out it tumbles and he has "stepped on my lines" and spoiled the joke for the teller.
1994, Hearings Before and Special Reports Made by Committee on Armed Services of the House of Representatives on Subjects Affecting the Naval and Military Establishments, Contributor United States. Congress. House. Committee on Armed Services, page 71:
Mr. KYL. Thank you, Mr. Chairman. […] do you want to take any additional testimony before we get to questioning? I have read the statements. / Mr. SKELTON. I think, as I understand it, I was told that the other gentlemen were here to answer questions. / Mr. KYL. Fine. I didn't want to step on your lines there, but I have read the statements and find them to be good and cooperative.
2020, Tom Lisanti, Carol Lynley: Her Film & TV Career in Thrillers, Fantasy & ...:
Carol was unhappy with Buttons mostly because he had the habit of stepping on her lines, intentionally or not. It throws actors off when another begins speaking their lines before they have finished saying their dialog and it diminishes their part.
