The fact that the NFL is even considering a settlement makes me think their case wouldn't be as much as a slam dunk in federal court as they think. I'm sure Harvey has informed them of this. Its not whether he deserves a longer suspension or not but comes down to how the PCP is worded and how its precedence for violations of this sort are written.
Or, the NFL is aware of the optics of this mess and just want it to go away without offending anyone. They want to look like they actually care and not let the stink linger.
