Sentence Correction (SC) | Jimmy Hill, a player, manager, and pundit, who had been credited with

mrinal0308 - explained it clearly. Just adding to that.

In gmat, whenever you find had/had been + verb, it means a past perfect tense. A past perfect tense talk about an event that is relatively in past of a past event. Best thing to sort such situation is that you create a timeline for all the verbs in the sentence.
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