A Perfect Fail!
No one likes a failure but it does happen, especially, with tennis string.
This is the perfect fail if you are using natural gut string. You can see the natural fibers of the string have been unraveling and finally reached the point where the stranding could no longer handle the impact of a ball hitting that area.
Natural gut and some multi-filament synthetic strings will exhibit this failure mode. The great thing about natural gut is that it plays better longer than other string materials.
The problem is that it is quite difficult to quantify “better” but it is easy to quantify “broken”. I recommend, if you are using natural gut, play with it until it breaks or the “fraying” is so bad you know it won’t last another match.
The use of Sting Savers can extend the life of natural gut string and will not affect the “feel” of the racquet.