George B. Schaller in his much acclaimed book - The Deer and the Tiger :

"One of the manifestations of the early part of the rut is the "sore neck: (J. Bombay Nat. Hist. Soc., 1921; Morris, 1988) or"sore spot." On the ventral surface of the neck is a line of hair, somewhat darker and less sleek than the surrounding pelage, which runs down the mid-line from the throat to the lower part of the neck. At the begining of the rut, the hair falls out at the terminus of this line, and the skin seems to slough off, forming a circular area about one to two inches in diameter which is bloody in appearance and exudes a seous fluid, "a kind of whittish looking oily or watery substance" (Thom, 1937). The area around the sore spot is sometimes swollen, and Kemp (1914 [quoted in J. Bombay Nat. Hist. Soc., 1921]) observed that hair is occasionally rubbed off over an area as large as eight inches long and six inches wide. I noted the first sore spot on November 15 and the last one on December 15. many sore spots began to heal during the first half of December, and by January the only evidence of them was an area of pinkish skin lightly overgrown with hair. Sore spots were not seen at other times of the year at Kanha, but in Kaziranga Sanctuary two stags and a hind all had them on May 3......."

This is typical to Sambars but not limited to South. Good job in clicking this sore spot with the leaf touch it. I would have been happier if the head of the Sambar were visible. Good documentation Vikram!