There are actually at least 2 kinds of 'sarong' as used in South-east Asia --one for wearing for both men and women as a kind of wraparound 'skirt' and one for just drapping on the shoulders, which as worn by females is called a 'selendang'
Sarong is not a primary combat weapon. You are not going to unwrap your 'skirt' to fight, are you? It may even be misinterpretted. It is usually the 'selendang' (in the Thai, Burmese cultures, it is called differently) which comes in useful in an emergency. In the rural areas, it is used as a blanket, carrying babies, etc.
In combat, it is used for distraction, restraining, hiding a small weapon. It is an art in itself.