In a sentence, the main verb refers to the action that is directly performed by the subject or related to it, which is usually placed right after the subject. This means that to identify the main verb it is important to understand the subject of the sentence. In the case of sentence "In addition, the research indicated that girls were more likely to get hurt and twice as likely to have a concussion", the subject or agent performing the action is "the research", this implies the main verb of this sentence is "indicated" as this is the action performed by the subject. Also other verbs such as "were", "get hurt" or "to have" are part of the object of the sentence but not the main action or verb.
