Looking forward to her first experience of love-making, Juliet has a hot blush and so she implores Night to hide her untamed blood, which is beating in her cheeks. The metaphor she uses is taken from the practice of falconry, in which an "unmann'd" (untamed) hawk is controlled by hooding it. Once hooded, the hawk is less likely to "bate," beat its wings wildly, when it is handled by a man.
Hood on a Goshawk Source:
M-J Hoods Gallery