He was bouncing a yellow tennis ball against the plexiglas wall of the tram stop.
I could start a story off that action. But better yet, I can describe a character. What do you see if I say he was all alone, dressed completely in black? Do you imagine a motive for the ball-bouncing is rebellion or disconcern for the inconvenience of others?
Now picture him in a white polo with a group of friends. Do you see him as a sporty showoff, the leader of a gang of rich kids?
What if I said he was older, perhaps thirty-five, in mix-matched clothes, insignifcant in the crowd, except for this action? Why is he bouncing the ball? Has he lost his job and is releasing some stress? Is he bored? Is he angry?
Personally, I like it when the character pushes the story. Let an action create a character, which then creates the story. I'd love to hear your version of the ball-bouncer!!!