Attacker (ZX81 Cassette 50 Game 8)

What am I supposed to do here? Am I the attacker? Or the attacked? Which one of the moving shapes on the screen is me and what do they do?

Your guess is as good as mine. I’d love to know. Any ideas gratefully received. A video might help:

See the Commodore 64 version of Attacker
See the ZX Spectrum version of Attacker
See the Amstrad version of Attacker
See the Atari 8-bit version of Attacker
See the Acorn Electron Version of Attacker