Wiktionary
prolly
adv. (context colloquial slang notably Internet slang English) (eye dialect of probably English)
Usage examples of "prolly".
Now you take the average vee-hikel, you jump that mother ten feet from here to there, and what you got, you got like a four-hundred-dollar repair bill and you prolly got a whiplash to go with it.
Liddell says he were that wore out after being out all night on an errand, he prolly fell asleep somewheres.