Final answer:
The sentence should use the adverb "well" instead of the adjective "good" to correctly modify the verb "played," resulting in the fixed sentence: "Mayor Quimby's team played well at the championships."
Step-by-step explanation:
The problem with the sentence "Mayor Quimby's team played good at the championships." is the use of the adjective "good" instead of the adverb "well."
The corrected sentence should read: "Mayor Quimby's team played well at the championships."
Adverbs describe how an action is performed and should be used when referring to verbs, while adjectives describe nouns. In this case, "played" is a verb, so it is appropriate to use "well" instead of "good."