Mystery Bird Quiz #6

This afternoon while I was out birding around the University Park Airport, I spotted an accipiter harrassing an adult Red-tailed Hawk. My binoculars were in the back seat, but I had my camera nearby so I started taking photos of the bird even though I wasnt quite sure what accipiter it was yet. Soon the bird flew off and out of sight. When I got home I quickly downloaded the photos so I could figure out what species it was. Some of its field marks were very confusing, so I figured I would put it up as a mystery bird quiz to see if I could stump anyone else. Take a look at these photos and then leave you answer and an explaination as a "comment" on this post. Once some answers are in, I will provide the correct answer and an explaination in another post. Have fun!