Assault in the Third Degree comes in two major "forms. " The first, NY Penal Law 120.00(1), is fairly simple and straight forward.In fact, some of the most vicious assaults occur when a dangerous instrument is used. Assault in the third degree is the lowest tier of assault charges. It occurs when someone inflicts physical injury – a bodily impairment or substantial. The vast majority of assault cases in New York are in the third-degree, which is defined as one individual intentionally causing physical injury to another. New York Assault Lawyer: There's a wide range of assault laws in NYC. Learn more about felony and misdemeanor assault charges in NYC here. Assault in the first degree occurs when you intentionally cause serious physical injury to another person using a dangerous weapon or instrument. Assault in the first degree is the most serious of the three offenses.