Linebackers?
Mostly, they disrupt things.
...like elegant football plays, dreams of fame, record-setting performances and thoughts of having a uniform at the end of a game that isn’t covered in mud, grass stains and occasionally blood.
When playing, I’d generally figure I and the rest of the defense were at an optimum when the opposing offensive huddle was rife with complaints, cussing and hard glances. If we had the coaching staff swearing, jumping up and down and shouting at their own players and/or the officials, we were truly excellent.
...but then, we’d conspire to REALLY get ‘em upset.
(This same role applied to practices against our own Offense and coaching staff. Worst football field fight I ever had was with my school’s All-Star QB after I’d dumped him on three successive plays during practice.)
Linebackers run the defense (defensive quarterbacks).
Experience.