What does the slang phrase guhn down a yard mean?

The phrase "gun down a yard" is not a common slang phrase and doesn't have a widely accepted meaning. It's likely a made-up phrase or a regionalism with a specific meaning within a particular group.

It's possible that it's a variation on:

* "Gun down a block/street": This phrase means to kill multiple people in a single location, typically referring to a violent crime or gang activity.

However, without more context, it's impossible to know for sure what "gun down a yard" might mean.

If you heard this phrase in a specific context, please provide more information so I can help you understand it.