What sport has Curley “done quite a bit in”?

Curley has "done quite a bit in" boxing.  He has done a
great deal of boxing.  This is actually important in the
book.

Curley's ability to box sort of feeds in to his
personality.  He is a very arrogant and aggressive person.  He likes to pick on people
with a combination of his boxing ability and the fact that his father owns the ranch. 
These allow him not to have to worry about people beating him
up.

This arrogance gets him in trouble when he goes after
Lennie and gets his hand crushed.