It's rude to discriminate based on age
Luke is playing chess in a public park against strangers who come and go.
Luke wants to practice against good competition.
A child attempts to sit across from Luke hoping to play him and Luke lets the child know that it will be just one quick game.
Luke denies the seat across from him as a child attempts to sit down to play him stating to the kid that he is looking for healthy competition.
The child has fun and learns a few tips and tricks that Luke teaches him.
The child feels embarrassed and stops playing chess entirely.