You have been cited under § 1.07 of the Public Courtesy Code: Leash Obstruction
THE LEASH IS A TRIPWIRE.
Your dog is on one side of the sidewalk. You are on the other. Between you runs fifteen feet of retractable line at shin height, and a stranger is about to discover it the hard way. Reel it in. The dog has no opinion on this.
This is not a fine. There is no fine. Think about what you did.