The Gemara tells us that according to Rebbi Yehudah "Gad only means Avodah Zarah (and not just Mazal)."
If so, how could Leah have called her son "Gad," saying "Ba Gad"!
Peretz, Yerushalayim
The source of Rebbi Yehuda's statement that "Gad" only means Avoda Zara is a Pasuk in Yeshaya. This does not prove that Gad was the name of an Avoda Zara when Leah called her son Gad. Further, even if it were an Avoda Zara at the time, if it was also used as a name of a person before the Avoda Zara came about, it would not be prohibited to use that name (see CHAVOS YAIR #1, Hasagah 11-12).
Kol Tuv,
Yaakov Montrose