Watch the video carefully and see if you see what I see.
At 6:25 the lionfish is to the left and the octopus is below it and to the right, then there is an edit and you see the spear starting to manuveur for a strike, if you watch closely the lion fish jumps before the spear comes close (the octopus is now below and to the left of it), then the spear hits the lion fish and pulls it away with the octopus already attached to the lionfish.
What appears to me is the octopus strikes the lionfish just a moment before the spear does. (this is the jump the lionfish does just before it is speared)
Some are interpretting the octopus going after a speared lionfish, but the reason I posted this is because it looks to me like the diver speared a lionfish an instant after an octopus hit it. If the diver with the spear had waited another few seconds to strike the lionfish, this would be a clear video of the octopus hitting the lionfish, but things happened so quickly it's easy to see it either way.
But I think the octopus hit the lionfish first then the diver speared it and the octopus is saying, no way Jose, I had first dips and is fighting to keep his meal.
Watch it a few times and see what you think.
I should have titled this thread "do octopus hunt lionfish", I have no doubt they would eat one if fed one, I think they'd eat a hot pocket if fed one, but this video seems to show one hunting one.