Doesn't say, but the doe could have seen its reflection in the glass and been trying to fight with itself. The "sudden" presence (from the deer's perspective) of a human right there was additional cause for fight. :shock:
On the other hand, deer could be mounting a sudden initiative against humanity. We should arm ourselves and go carefully when we are in the woods. My wildlife biologist friends tell me that it is a good thing that deer do not carry knives or else there would be a lot of hunters with their throats slit.