Self employed

I'm in a similar situation with reselling some of the football tickets that are part of my season ticket package for games I can't go to.

 

- What is the distinction that determines whether it is a  hobby or a business? Do they just take my word for it, or is there an income threshold or something concrete I can reference?

 

- To clarify - if it's a hobby and not a business, does that mean I don't get taxed on the money from reselling the tickets at all?