The sentence that contains an action verb is the following one: The band should have been marching toward the end zone.
An action verb is a verb that expresses a physical or mental action. They tell us what the subject of the clause is doing whether it is pshysically or mentally. In this case, the verb is "march" which, according to the Merriam Webster dictionary, means "to move along steadily usually with a rhythmic stride and in steps with others".
