Not at all. That's like saying that "a boxer is someone who does boxing" is circular. It's only circular if you define boxing as "that which is done by a boxer"

Not at all. That's like saying that "a boxer is someone who does boxing" is circular. It's only circular if you define boxing as "that which is done by a boxer", instead of "striking an opponent with such-and-such ruleset, this equipment, etc. in an event sanctioned by such-and-such organization."