That might be a firearm in the state of NJ. Just Saying
"Firearm or firearms"...shall also include, without limitation, any...weapon of a similar nature in which the propelling force is a spring, elastic band, carbon dioxide, compressed or other gas or vapor, air or compressed air, or is ignited by compressed air, and ejecting a bullet or missile smaller than three-eighths of an inch in diameter, with sufficient force to injure a person. A reasonable person wouldn't think it includes a rubber band gun, but naturally it was written broadly enough that an ambitious prosecutor could make the case.
I was sort of joking, I had forgotten about the "elastic band" clause. At that point you're left arguing the "with sufficient force" clause, which, admittedly, would appear to be where Airsoft lives...Of course, an ambitious prosecutor could nail you for a crossbow or bow, too(the stave is a spring, after all, just not a coiled one).