Aruch HaShulchan 167:31 and Be'er Hataiv 167:22 both say that it is forbidden to throw the (Challah) bread. I have heard that there are some people (I heard that there are some Rabannim who do so) ...
When you make Hamotzi on Shabbos you use the top Challah. However, on Friday night you use the bottom. Therefore, so as not to pass over the Mitzvah you hold the bottom one closer. My question is why ...