“Announcing” is in the form of a participle that’s working as a modifier: “Anderson remembers Greinke announcing.”
The adverbs are also a bit, well, meek. “Suddenly” is OK. But combined with the adverb “once,” it delays and weakens the action. Plus, “once” is a time element in a sentence that already has a time element — that stuff about “during a dreadful season.” Sure, you can use two time elements in a sentence, but usually it makes it flabby.
The problems with this sentence all occurred because Posnanski wanted to squeeze in a lot of information very fast. But often a writer would do better to break up the information into two or more sentences: