Sorry for the delay. I was feeding the mosquitoes down south for the past 2 nights/3 days.
I can answer your question with some of my own. What color(s) was it? Where was it? And how was it flying?
The basic ones it could be are: red-tailed hawk, turkey vulture, or Cooper's hawk. It could be something else, but those are 3 of the most common. But the habitat (or just the area where you've seen it) and the behavior are some of the ways to identify hawks without pics.
Here is a list of all the birds that have been seen in NJ with links to Wiki pages for them. The sections you want are New World vultures; Kites, eagles, harriers, and hawks; and Caracaras and falcons. They're all on the fourth line in the first paragraph of links in the table of contents. So have a look, and see if any of those look familiar.
The 1000 character limit prevents me from typing too much. Lucky you.