SATURDAY: Box office continues to slump as moviegoers stay away from theaters for another weekend, showing yet again how the lack of big tentpole pics can’t drum up excitement for all film fare. But Sony scored yet another No. 1 opening — its 10th this year — when The Rock’s Gridiron Gang gritty football flick based on a true story opened with $4.8 million from 3,504 theaters Friday. The pic which cost only $30 mil to make received a 30% bump for Saturday’s business, so the film ended the weekend with a $15 million weekend bow. But the film had, in the word of one box office guru, “crazy good exits”: an A Cinemascore, A+ under 18 from both men and women. By contrast, the exits for Universal’s The Black Dahlia was only a D+. Still, the Hollywood true-crime mystery movie had good per-screen averages; playing in only 2,228 theaters, the film earned $3.7 million Friday but only bumped 6% for Saturday for what was a $10 mil weekend. The Paramount/DreamWorks/Lakeshore debut of the latest Zach Braff relationship movie The Last Kiss did passably considering it was only playing in 1,357 theaters, earning $1.8 mil Friday for a $4.6 mil opening weekend. Fox’s kiddie fare Everyone’s Hero failed to pull in more than $1.6 mil Friday from 2,896 theaters for what was only a $6.1 mil bow. Rounding out the top 5 movies, Sony’s The Covenant was down 47% its second weekend out, taking in $1.4 mil Friday for an additional $4.7 mil. Meanwhile, Sony overtook Disney in market share with $1.15 billion. The only other interesting take on this weekend was moviegoers’ rejection of Old Hollywood-themed fare.  Focus Features’ Hollywoodland collapsed its second weekend out — eking out only $800,000 Friday from 1,551 theaters for only $2.7 mil second weekend out. So much for Ben Affleck’s comeback: a critical success, but not a box office one. (All weekend figures include Sunday estimates.)