Actually he punched his girlfriend's ex for spitting on her. Something that I have a difficult time criticizing him for doing. I know I would punch someone for spitting on my girlfriend/wife.
As far as the pot goes....the article points out that Melo has passed every NBA administered random drug test and the olympics drug test. So the evidence is mighty shaky to go forward and condemn him. He might actually being telling the truth.
I would rather jump his case for being stupid enough to take a carry on without checking out all the pockets first. Travelling by air has gotten way to tight security wise to not know exactly what is in every pocket of every thing you are taking on the plane.