David, in the 2013 preseason esks/leos post game comment thread, wrote:* Thought it was quite a lively crowd for a Friday night preseason game. 26,733 on hand which was the 3rd highest gate in the league this year.

Yes, there were no shows and likely a lot of freebies in the crowd, but still a good sign. The concourse was packed at half-time like it was a regular season game and LONG line-ups for merchandise at the souvenir stands.

I haven't read a whole lot of media accounts of the game so I'm not sure how loudly the following fact has been trumpeted, but Friday's game represents the largest attendance for a Lions preseason game...
since 1990! That was basically the tail-end of BCP's status as a novel venue and the point at which the effects of Bob Ackles' departure to Dallas were first felt. So if the crowd was indeed lively (and I agree it was), well, it was the largest such one in about a generation!
I had a look, over the history of the 18-game season era dating back through 1986, at how regular season average attendances correlate to the preseason attendance. It's not that strong a correlation — the scattergraph does show some scatter — but if you try to project the 2012 average attendance from the 2012 preseason attendance and the 1986-2011 data, you get a result of 30,713, compared to the actual average of 30,356: not too bad. Buoyed by that close agreement I've tried to project this year's average in like fashion and I get 31,940. That's still below the 34,083 peak in the final season of the 2002-2008 Ackles II era but it seems to indicate things are still going in the right direction re: regular season average attendance:
2008...34,083 (BCP I)
2009...28,610 (BCP I)
2010...24,327 (Empire)
2011...29,725 (Empire/BCP II)
2012...30,356 (BCP II)
2013...31,940?????
...
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Sports can be a peculiar thing. When partaking in fiction, like a book or movie, we adopt a "Willing Suspension of Disbelief" for enjoyment's sake. There's a similar force at work in sports: "Willing Suspension of Rationality". If you doubt this, listen to any conversation between rival team fans. You even see it among fans of the same team. Fans argue over who's the better QB or goalie, and selectively cite stats that support their views while ignoring those that don't.