Hoodoo folk have their slang and vocabulary and I have this suspicion that people don't know what "throwin' for" means. I think most people correctly interpret it to mean doing work against another person but what they may miss out is the literal meaning.
The term "throwin' for" literally means taking some powder, such as hot foot powder, and throwing it at the back of a person when they pass you. Ideally a worker wants the powder to hit that person's back but as long as it is in done quickly after they pass then it should be effective. A very simple work that is done when you dont' want someone to make a return visit is to take salt and pepper in your hands and throw it, or even sling it in the direction they left or else in the direction your porch or sidewalk faces and then sweep that mess out into the streets. You want to do this like immediately as the are leading. Do not wait for them to get in their car and drive off. As soon as they walk out that door grab your salt & pepper and your broom and have at it!
Workers "throw for" other people usually when doing enemy work and work to banish or hot foot people.