The phrase "hadst a fling at" is an archaic way of saying someone took a quick shot or attempted something quickly. The word "hadst" is spelled with an "-st" at the end because it is in the second-person singular form and a part of the past indicative tense of the verb "have." The IPA transcription of "hadst" would be /hædst/. Similarly, the word "fling" is pronounced as /flɪŋ/ and means to throw or toss something quickly. The phrase as a whole reflects an old-fashioned use of language not often utilized in modern usage.