import re


def match_crash_field(page):
    """
    Extract the crash number from the content of the fatality page.

    :param str page: the content of the fatality page
    :return: a string representing the crash number.
    :rtype: str
    """
    crashes_pattern = re.compile(
        r'''
        (?:
        (?:Traffic\sFatality\s\#(\d{1,3}))
        |
        (?:Fatality\sCrash\s\#(\d{1,3}))
        )
        ''',
        re.VERBOSE,
    )
    matches = crashes_pattern.search(page)
    if not matches:
        return None

    non_empty_match = [match for match in matches.groups() if match]
    return non_empty_match[0]