Porcupine Pufferfish damaged!

[fishoholic]

Triggers are fairly aggressive, I've seen them bite before and they can be quite nasty, so I would lean towards the niger trigger as being the culprit.

I would keep the puffer isolated until he heals (should heal on his own as long as the water quality is good) and choose between keeping the trigger or puffer and sell the one you don't want to keep.