A coach on the sidelines or in the pressbox electronically transmits instructions for the next play to the quarterback, who relays the information to his teammates in the huddle. On Sunday, when Joe Flacco (Baltimore) and Colin Kaepernick (San Francisco) back away from centre and start barking instructions, they are likely changing that play. They've determined the original call won't be effective against the defensive set, or detected a vulnerability a different play may be better suited to exploit.
Defined as "any swift, vigorous attack, barrage or defeat," this term does not refer to the onslaught of new TV commercials before, during and after the game (nor the onslaught of complaints to the CRTC from viewers forced to watch Canadian ads instead). In football terms, a defence blitzes by sending a linebacker or a defensive back (or both) along with the usual three or four lineman, hoping to overwhelm the offensive linemen and tackle, or "sack" the quarterback.
Wide receivers are generally bigger and sometimes faster than the defensive backs assigned to cover them. Still, a successful pass from quarterback to receiver depends largely on timing. To disrupt that, cornerbacks may attempt to impede the receiver by giving him a hard nudge just as he comes off the line of scrimmage. Slowing down the receiver slightly better enables the cornerback to turn and run alongside him downfield.
This San Franciso play is all the rage: Kaepernick receives the ball from centre, determines in a nano-second what the defence is up to, and either hands the ball to his running back, takes off with it himself, or throws it. Quoting The Wall Street Journal: "Those plays – or even just the threat of them – are quickly turning the mechanical NFL into something more like frenetic, world-class rugby. For a new generation of football addicts, it's the equivalent of last year's Higgs-boson moment, when particle physicists finally found the tiny atomic material that forms the universe."
The area between the 20-yard line and the goal line being protected by the defensive team. Effectiveness in this area logically factors into a team's capacity to win. In the regular season, Baltimore ranked fifth overall in the NFL, scoring a field goal or touchdown 61.2 per cent of the time it reached the red zone. San Francisco was 15th, at 54.7 per cent.