Not being there and observing it, and so not knowing how it actually went, the party who bite the other person's finger off was clearly wrong for doing so.
However, several things seem to be being missed in the insightful commentary above, by our resident analysts here on EO:
First, the guy who got his finger bitten off (the bitee) actually first punched the biter in the nose ..... and admitted to it (because he supposedly felt "threatened)
Not that that excuses the biter's conduct - it doesn't.
Second, if you viewed the KTLA video piece, the one eyewitness being interviewed stated very clearly that the person who had his finger bitten off was clearly the aggressor ...... dunno who she was, or what agenda she had (if any)