It's basic contract law, not necessarily my opinion. (For the record, I believe he's guilty, and I believe he's a sick fuck, and I'd love to have a chance to cattle-prod his balls.)
Vick signed a contract. If the contract stipulates he must refrain certain activities, and maybe (definitely) includes a catch-all phrase that would cover all the bases in the event the 'certain activities' are not set out specifically (i.e. must test negative for steroids, weed, opiates, etc.) that leaves it up to the interpretation of a jury should he attempt to sue in the event he is fired as to whether or not his extracurricular activities did, in fact, have negative repercussions on his employer.
And, also, I don't how much employment law would really apply here as far as his "rights" with his "employer" - he's under a contract and the contract, as long as it isn't deemed illegal or that any party signed under duress, would supersede over employment law.
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