Get mad with one predicting Delaware setback (3,3)

I believe the answer is:

see red

I'm a little stuck... Click here to teach me more about this clue!

But I can't explain it at all! Could you help me understand?

(Other definitions for see red that I've seen before include "Lose temper like enraged bull" , "Be suddenly angry, as bull might" , "Become angry (colloq.)" , "Get furious" , "Be annoyed" .)

I've seen this clue in The Guardian.

Want a hint initially instead of a full solution? Install my app