In astrological tradition, the Rising sign (the Ascendant) is the sign that was on the eastern horizon at the moment of birth. It is often read as the "first impression" — the style someone leads with and the lens through which they meet the world.
With Sagittarius Rising, that first impression is often read as adventurous, candid, philosophical, and freedom-loving. As a fire sign, Sagittarius tends to give the outward manner a adventurous, candid cast, and tradition associates this Ascendant with a philosophical approach to new situations and new people.
Because the Ascendant depends on an accurate birth time, a Rising sign cannot be guessed from a birthday alone. These are the general tendencies astrologers associate with Sagittarius Rising — not a prediction, and not a substitute for the full chart that places it among the houses and aspects.
A general guide to astrological tradition — tendencies, not predictions. It describes the placement in the abstract and is not about any specific person.