drop the ball

(idiom) to neglect or forget to do something important which you were responsible for, causing it to be ruined

Example Sentence:

Thomas dropped the ball when he forgot to pick his girlfriend up at the train station. She was so mad that she returned to her hometown, ruining their vacation.

A: Hey, welcome to my party!
B: Thanks!
A: Did you remember to bring the beer? It was your responsibility.
B: Oh no, I dropped the ball and totally forgot.
A: Now we have no beer for the party! It’s going to suck!
B: I’m so sorry!

Media:

Similar idioms:

1. have a ball
2. behind the eight ball
3. start the ball rolling
4. bring it on
5. bring home the bacon