The field is condensed in the red zone, and defenses become more aggressive. As Bill Walsh once said: "...every defensive coach in the country is going to his blitzes about right there. The pass coverage, by and large, will be man-to-man coverage. We know that if they don't blitz one down, they're going to blitz the next down."
Of course, Tony Franklin knows the same. One of his favorite concepts in the red zone has become variations of his throwback screen (note: others may use different names for this screen...I will say throwback for simplicity's sake, but others may call it a solid, throwback, jailbreak, or rocket screen, and all refer to specific variations).