According to an article from Voice of San Diego, there is an email correspondence between the Mayor's Office, the City Attorney, and the Chargers that the City Attorney does not want released to the public -- at least not yet.
Author's Note: The speculation / theories below are solely those of the author, and do not reflect the opinions of Scott Lewis or anyone involved with Voice of San Diego.
Before proceeding, I recommend everyone read Scott Lewis' piece in Voice of San Diego. For those who don't however, here is the money paragraph:
"Whatever (City Attorney Jan) Goldsmith wrote - or whatever was said in response to him - is apparently so toxic and disruptive to the mayor's strategy in dealing with the Chargers that the city is taking extraordinary measures to keep it confidential.