[ConnorMcLeod]

"walk" in not a cs command, if you want to keep it as a custom command, then you need to return PLUGIN_HANDLE to prevent cs from throwing "unknown command" in player console.

I think you are confused with command +speed, this command is not hookable on server.
Maybe you have an alias "walk" in userconfig.cfg and you forgot about it ;)

If you want to keep the custom command, then i suggest to rename it to something not common, as amx_backturn or something like that.