Adam Levine -- Unlucky Strike ... Nails Fan In The Head With Mic (NEW VIDEO)

Adam Levine couldn't have imagined smashing a woman in the head with his microphone would actually make her love him more, but watch for yourself ... it totally did.

During Maroon 5's show in Toronto Monday night ... the sound guys were having trouble and Levine was pissed ... so he chucked the mic in frustration, which took a crazy bounce and nailed a female fan in the face.

Levine immediately ran over to check on Stephanie Green in her front row seat -- she was fine, and about to get better. Watch the vid ... Adam got pretty smooth, and most likely dodged a lawsuit in the process.

Must've learned that move from Jagger. There, we said it.