What kind of bird is this?

I live in Maryland. I went out to cut the grass the other day and was literally being dive bombs by these little fast low flying birds. They seemed very territorial. 2 or 3 were actually circling me at one point. I went out into the front yard and they followed me out there. I watched them for a while, and I never saw them land so I couldn't get a good look at them, but they fly very low and fast. Maybe have a little bit of blue on them. Kinda look like a Swallow, but Idk.