Bluegill got attacked?

[tadmaz]

I was fishing for bluegill, got this one hooked, 7.5", then either it got seriously caught in some weeds or a northern or musky might have bit onto this poor guy. Some bluegill were diving down and then it was tough to pull them out with all the weeds. It felt like I snagged a log and at first there was some fight to it, then just felt like a log, then after a minute there was no tension and I pulled this guy out. Any ideas as to what happened? (judging by the injury in the picture, oh and the injury was only on one side of the bluegill, not both sides)