BBA means Bachelor of Business Adminstration . As bba is the study and proper management of business. So in order to manage the business the person must have basic knowledge of the business. So BBA degree comes under commerce stream. I told commerce as Commerce is the BASE for the study of BBA degree as it is related to most of the subjects of commerce such as secretarial practise, Accountancy, statics,economics, organisation of commerce etc.
As commerce is the base for The further study of Accountancy as you should know who is a debtor , who is a creditoretc..which is necessary for running the business. As most of the subjects of commerce are related to BBA as well as Bcom so i would say that it comes under commerce stream.
But B.A means Bachelor of Arts comes under Arts stream. It doesnt include any accountancy, study of businessetc. But it includes the study of geography as well as study of Economics so i would say that Arts is slightly or very little related to BBA.