Ludum Dare 49 is also coming up from October 1 through October 4; you can use Lisp there as well if you like.
For 2d games, Fennel with LOVE seems to be a maintained and good choice. Are there some Scheme 2d frameworks similar to LOVE that are still maintained and offer also packages with e.g. collision detection or physics? I have had a look at [0], but many seem outdated.