What is the off-field rumor?
He was questioned by the police a couple of times about gang-related crimes out in California. Nothing of substance ever game of it, but if you do a Google search on “DeSean Jackson, Crips” you might find a few interesting links.
Connections to the crips. On Twitter, he openly supported a gang member in prison for killing a kid in a drive-by. The killer was a rapper on Jackson's record label.
He was also fond of flashing gang signs on the field.
If I'm running the team and investing tens of millions of dollar in these kids, that pic alone is reason enough for me to let him walk.