Final answer:
The opening sequence featuring a voice over about the Left Tackle's role is commonly associated with the movie "The Blind Side," where the significance of this football position is explained.
Step-by-step explanation:
The question pertains to a specific scene, likely from a film or television series, where the role of the Left Tackle in American football is explained via a voice over during the opening sequence. Although not explicitly mentioned, such a scene is a hallmark of the movie "The Blind Side," where Sandra Bullock's character explains the importance of the Left Tackle's position in protecting the quarterback's blind side.
This position is crucial because it safeguards the quarterback from getting hit by the fastest and strongest defenders who attempt to tackle him from his left side, which the quarterback, if right-handed, cannot easily see.