I got the idea for this game from the title of Kenta Cho's new game Deadly Balls Bounce. The game itself is inspired by Hundreds and Minesweeper.

Controls:

WASD - Move.
Left click - Tag ball.

Tag only the dangerous bellyballs to win the level. The dangerous bellyballs bounce off the edges of the screen, whereas the harmless ones wrap around.

If you want more videogame ideas like this, here's a shindan: http://en.shindanmaker.com/309864