80s/90s book where boy stumbles on game where aliens gamble their planets

Question

I don't remember much about it other than the setting. It's about a boy who one night stumbles upon some different alien races playing a game in which their civilizations will end if they lose. He gets involved in the game somehow and is hunted.

Answer 1

First thing that pops to mind is Interstellar Pig, by William Sleator.

From the plot summary:

When Zena, Manny, and Joe move into the cinder-block cottage next door, Barney is intrigued by their glamorous, exotic lifestyle. His fascination grows when Zena introduces Barney to their favorite pastime: Interstellar Pig, a board game in which the key objective is to finish the game with the Piggy card in hand.

Zena quickly briefs him on the rules: each player picks their character from a box of cards depicting different aliens. Every alien race has their own strengths, weaknesses, and IRSC (Interstellar Relative Sapience Code, with lower numbers favorable). When the time runs out, every home planet will be obliterated except the one belonging to the holder of the Piggy. Barney is amazed when the neighbors keep choosing the same character cards: Joe repeatedly picks water-breathing Jrlb; Zena always chooses Zulma, an arachnoid nymph; and Manny always picks Moyna, an octopus-like gas bag.

Answer 2

Could this be The Homeward Bounders, by Dianna Wynne Jones? From Wikipedia:

Twelve-year-old Jamie discovers a strange place in his hometown in which mysterious and demonic entities, known only as Them, are playing a board game with the entire world. Upon his discovering Them, They are forced to make Jamie a Homeward Bounder; this means he must constantly travel from world to world until he finds his home again.