drop the ball - Phrases/Idioms
The American Heritage® Dictionary of Idioms by Christine Ammer. Copyright © 2003, 1997 by The Christine Ammer 1992 Trust. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Make an error; miss an opportunity. For example, She really dropped the ball when she forgot to call back, or He dropped the ball, turning down their offer. This expression comes from sports where a player who fails to catch a ball is charged with an error. Its use for more general kinds of mistakes dates from about 1950.