If you start watching video at the 1:37 mark during the solo outro, Vinnie sweeps his right arm back across the guitar, and appears to take a couple of chunks out of the fin:
![Image](https://live.staticflickr.com/65535/50698824488_ba9aef928c_c.jpg)
If you look at the fin after the incident, you can see it appears to be damaged:
![Image](https://live.staticflickr.com/65535/50699654602_957bb9fcbb_c.jpg)
To watch the segment in slow motion, pause the video at 1:37, then you can move forward or backwards frame by frame using your "," and "." keys.
Clearly those early Jacksons needed some fortification!