Via Google search and consulting the Chicago Manual of Style, I have discovered that a colon not a period is supposed to precede a quotation when that quotation is a complete sentence or an independent clause. (A comma is used for a quotation that is not an independent clause or complete sentence.) Responses to my question have suggested there is no such rule. Does anyone see a way to reconcile these views? Are there circumstances when it is acceptable to put a period at the end of the sentence before the quotation or not? I ask because sometimes the quotation is more or less unrelated to the preceding sentence, and the result can look odd. Any guidance would be appreciated.
Example: Charles and Ben love to play basketball _ [period or colon?] "Suit up everybody; we've got a big game tomorrow!" yelled the coach.