http://law.onecle.com/new-york/penal/PEN035.15_35.15.html
New York Penal Code 35.15 says that " 2. A person may not use deadly physical force upon another person
under circumstances specified in subdivision one unless:
(a) The actor reasonably believes that such other person is using or
about to use deadly physical force. Even in such case, however, the
actor may not use deadly physical force if he or she knows that with
complete personal safety, to oneself and others he or she may avoid the
necessity of so doing by retreating; except that the actor is under no
duty to retreat if he or she is:
(i) in his or her dwelling and not the initial aggressor; or
(ii) a police officer or peace officer or a person assisting a police
officer or a peace officer at the latter's direction, acting pursuant to
section 35.30; or
(B) He or she reasonably believes that such other person is committing
or attempting to commit a kidnapping, forcible rape, forcible criminal
sexual act or robbery; or
© He or she reasonably believes that such other person is committing
or attempting to commit a burglary, and the circumstances are such that
the use of deadly physical force is authorized by subdivision three of
section 35.20."
Subdivision 3 of section 35.20:
" 3. A person in possession or control of, or licensed or privileged to
be in, a dwelling or an occupied building, who reasonably believes that
another person is committing or attempting to commit a burglary of such
dwelling or building, may use deadly physical force upon such other
person when he or she reasonably believes such to be necessary to
prevent or terminate the commission or attempted commission of such
burglary.
"
With that many people there (even if it was less) encroaching on his property, it was reasonable to assume they were going to burglarize his house, and possibly injure him or his family.
http://law.onecle.com/new-york/penal/PEN0140.10_140.10.html
Penal Code 140 defines what Third Degree burglary is. Basically, if he has a fence, and they go inside of it, he has every right to use deadly force to protect his property. If not, it's a little shadier, since he stepped outside, but I would guess that since he felt his family, and he himself, were threatened, he was allowed to do what he did, since it wasn't violent, and wasn't a use of deadly force. But hey, I'm not a lawyer
Also, the law doesn't cover reckless endagerment, which I believe is defined as "The state of being endagered; having a small blade lodged in your body."