Le pegó un par de puñetazos que le hicieron sangre y le arrancó el aparato de las manos. (Source)
This refers to a man and a woman fighting. How do I know who "le" refers to? Is it the woman or man?
There is no way to know who is being attacked, or perpetrating the aggression, with that phrase alone.
The sentence uses a pronoun le which is valid for both masculine or feminine subjects.
(...) 2. pron. person. 3.ª pers. m. y f. Forma que, en dativo, designa a la persona a la que se dirige quien habla o escribe.
Update: the news article that you included in the comment shows the context to know that it was a woman who got hit —cowardly so, from a man punishing her with a politically loaded reason.
Regarding the grammar question, on the possibilities of the language, to be explicit about the gender with that sole sentence the femenine third person pronoun la source would suffice
The sentence would have been unambiguous had it been written to read:
Le pegó un par de puñetazos, que la hicieron sangrar, y le arrancó el aparato de las manos. [ made her bleed ]