Something huge just popped into mind for me...
As seen in the first episode of volume 4, there are Geist Grimm that can possess things and many have speculated that there was a Geist inside the knight inside of the white trailer. After a while of thinking... back when Winter Summoned a Grimm to fight and do her bidding, the Grimm she had summoned was primarily white and partly blue, likewise when she summoned small nevermores to fly towards Qrow, they were white...
Now thinking back to the white trailer along with Winter's summoning and the Geist from episode 1... What if, the reason that Knight was attacking Weiss is because her farther in anger had decided to "test" Weiss to see if she was worthy of even defying him? If he's defeated a Geist before then he could summon his own geist to do his bidding and potentially kill (probably not kill but atleast knock the confidence out of her completely) Weiss. Reason I pointed out the whiteness of the summoned Grimms is because when Weiss did her final hit against the Knight, the aura that seemed to leave it was purely white rather than black like when the Geist left the stone.
Am I over-analysising or am I onto something?.. Jacques seems like the type of person to possibly do that or if not him then maybe her mother, though Weiss claims he "always came home furious, which made for a very difficult childhood"...