What is the passive verb in the following sentence?: The ball was thrown by the quarterback who was running from the linebacker.
'was thrown' is the passive verb.
"The quarterback threw the ball" has an active verb "threw", where the quarterback is the subject and the ball is the object. When it is turned into the passive form, the subject then turns up in a "by" phrase - "by the quarterback".
The verb "was running" is active - it is the quarterback who was running.
See Passive verbs for a formal explanation