My "their" team comment wasn't aimed at the team, it was aimed at Joe Six-Pack mouthing off about "my team".
On one level "my team" could just be a common verbal shorthand for "the team I like to watch and root for" -- annoying, but not an indicator of mental illness.

On the other hand, if they are claiming some sort of affiliation with/membership in/influence over/ownership of the team despite not being an NFL franchise owner
*, player, coach, on-field cheerleader (shouting from the stands doesn't count

), or even the waterboy, then
that is a sign of mental illness IMHO.
* Includes the 364,122 stockholders of Green Bay Packers, Inc.
Scott