(And everyone knows that Equity trumps English... 
LOL!
Anyway, looking back to grammar lessons... If you are refering to the title, it should be capitalized, as in "I was hired as Production Stage Manager..." (like it would be "I served as Director of Operations/President of the United States", etc). If you are refering to the job function - "I am a stage manager" - it is a general position and it should not be capitalized.
Can't think of a situation stage management would be capitalized except the title of a class, ie. Stage Management 101.
NB: grammar errors abound in all other aspects of the previous sentences!
