In the 7th book, when Ron is eventually able to tune in to the Potterwatch radio station with the password "Albus", they mention that there was an attempt to arrest Hagrid for hosting an event at Hogwarts in support of Harry. This means that he remained at Hogwarts for a number of months into Harry's would-be 7th year.
Why was Hagrid allowed to remain at Hogwarts for so long, seeing as he is half giant, associated with the Order of the Phoenix, and a known close friend of Harry's?
Any of these things alone would be possible reasons for Snape, under Voldemort's orders, to expel him from the school, or otherwise attempt to arrest or even attack him.
My only guess is they had hoped Harry might attempt to return to Hogwarts to visit Hagrid? Is there anything in the book mentioned that might give a solid hint about the reasoning behind this?