byplay

Bobby grabbed the lapels of the man's coat. Three pedestrians noticed the byplay; they promptly scattered.
"Try me," Bobby said.
"Now, Bobby"
"Who the hell are you?"

Source: Alone, Lisa Gardner

Background: A scandal implicated Bobby, an embattled officer, to such an extent that he had to go on immediate paid leave. When he was walking alone down a narrow alley today, he noticed the footsteps behind him. Being sure that he was not imagining things, he turned back around and confronted the tail.

Hi, byplay basically means " incidental activity performed by an actor for dramatic effect" (link). In this instance, however, it seems to have an extended meaning. I guess it means "a street incident in which you aren't involved". Am I right?

I like this definition:

byplay (plural byplays)

1. (theater) Any action, carried out onstage during a performance, apart from the main action.

I think you need to take it literally, rather than "figuratively." The pedestrians notice this as one of the many things going on on the street apart from "the main action" - i.e., the street itself with cars and such. To the reader, it just gives the impression that the street is like a stage with lots of little individual stories playing out on it; the fight between Bobby and the man is just one of those little stories.

Thanks, lucas. Reminds me of a viral clip where a guy breaks up a subway fight while eating a bag of chips. I guess I can use "byplay" to describe subway fights/arguments which break out so frequently that people stop making a big deal out of them.

Just notice that it's not exactly a common use of the term. You'd be engaging in metaphorical language whenever you discussed "by-play of the subway" in that manner.