foul up phrasal verb informal ( see also ↑ foul )
1 . to do something wrong or spoil something by making mistakes ⇨ foul-up :
We can’t afford to foul up this time.
foul something ↔ up
Glen completely fouled up the seating arrangements.
2 . foul something ↔ up to make something very dirty, especially with waste:
He lit a cigarette and started to foul up the air with stinging yellow smoke.