From what i know, your left foot is best as your "forward/lead foot" if you are Right-handed. The right foot is the lead if you are left handed. They can be interchangeable; but that is highly not recommended for those whom aren't familiar with basics and/or advanced maneuvering. ++Oppinion++: As a matter of fact the only real reason a boxer may do so is if fighting a certain opponent with with a style that would be put at a disadvantage by changing your stance. "Isaac's the name, the chins my aim"