IPA: /ˈɡrʌbɪli/
KK: /ˈgrʌbɪli/
In a dirty or unclean way.
The children played grubbily in the mud after the rain.
Grubbily → It is formed from "grubby" (from Old English "grub", meaning dirty or filthy) and the suffix "-ly" (meaning in a manner of). The word "grubbily" means in a dirty or filthy manner.
Think of the word 'grubby' which means dirty, and remember that 'grubbily' describes doing something in a dirty way.