'A', a resident of Delhi, files a suit at Delhi for infringement of Trade Mark by 'B', a resident of…

Section 134(2) of the Trade Marks Act, 1999 lets a plaintiff sue for infringement where he resides or carries on business, but in Indian Performing Rights Society v Sanjay Dalia (2015) the Supreme Court held that where the plaintiff also carries on business at the place where the cause of action arose, he must sue there. So the Delhi court "has jurisdiction only if 'A' does not have an office in Mumbai". It is wrong to say that Delhi has jurisdiction unconditionally or none at all, and leave of court has nothing to do with it.