For instance, is it grammatical?
I looked from the window and spotted a person. It crossed the street.
For instance, is it grammatical?
I looked from the window and spotted a person. It crossed the street.
No, in this context a human should be refereed to as "he", "she" or "they".
"It" is used for inanimate objects or non-human animals. Although, if you knew the gender of the animal, you might still use he or she in some circumstances.
Thus
I looked from the window and spotted a person. They crossed the street.
I looked from the window and spotted a man. He crossed the street.
I looked from the window and spotted a girl. She crossed the street.
but
I looked from the window and spotted a dog. It crossed the street.
I looked from the window and spotted a car. It drove down the street.
however, possibly
I looked from the window and spotted George's mare. She galloped down the street.