Let the side down
Definition 1 of 1
Pro Tip 1/3Team Responsibility
Expresses letting down a group you're a part of, emphasizing collective responsibility over individual. 
Despite working hard, when the project failed, we all felt like we let the side down.
Pro Tip 2/3Emotional Impact
Carries feelings of guilt or shame for not meeting expectations of a group or team. 
After forgetting my lines in the play, I couldn't shake the feeling that I let the side down.
Pro Tip 3/3Metaphoric Use
Can be used metaphorically, not just in actual sports or team contexts. 
Not arguing the client's case effectively, the lawyer felt he had let the side down.