I think that word is what may be messing ppl up here. It being called a "hit" implies Big U paid money and sent Holder and this was some planned/thought out mission.
I think it plausible U just set shyt in motion to where Holder would kill Nip, no money changed hands, just manipulated shyt. Whisper in Holder ear, knowing he would go off etc.
It's also plausible U had nothing to do with it and Holder was just a reckless crash out.
Personally, I dont think Holder even thinks about killing Nipsey if he thought U wouldve had a problem with it. Ppl tried to paint holder as crazy, but some posts in here seems to put that idea to rest. I can see a world where U let it be known that Nipsey was touchable.