Overheating. Starting a cold engine and running it like a raped ape cold. Lack of lubrication. Defect. A very misfortunate detonation. Cooking oil. Etcetera. Several things can cause it. Other damage should be evident if it's something like an extremely lean condition. That piston looks like it got pretty hot in that picture.
2013 V Star 1300 Deluxe
OEM Tall Sissy Bar
Memphis Shades Fork Deflectors
Bridgestone Exedra Max Belted Tires
Baron's RSTD 7308 bar