Every time I have heard the term "speedball" used in a sentence, it has been when someone is using either methamphetamine mixed with heroin or cocaine mixed with heroin.. and mostly when the ROA is via intravenous injection. I suppose you could speedball if you smoked your substances or even if you shoot up one and smoke the other, but every time I have heard the words "you down for a speedball?" the reply in most cases is "yeah bro, you got a point?". Point - syringe. I have also heard the term "goofball" to describe the same thing.