2018 New York Laws
VAT - Vehicle and Traffic
Title 7 - Rules of the Road
Article 34-B - Riding Horses
1265 - Wearing of Helmets.

§  1265.  Wearing of helmets. 1. No person less than eighteen years of
  age shall ride a horse unless such person is wearing a helmet meeting or
  exceeding ASTM F1163 (Safety Equipment Institute  certified)  Equestrian
  Standard.  For purposes of this section, "certified" shall mean that the
  helmet's manufacturer agrees to the rules and  provisions  of  a  system
  that  includes  independent testing and quality control audits, and that
  each helmet manufactured by such manufacturer is permanently marked with
  the certifying body's registered mark or logo before such helmet is sold
  or offered for sale. For the purposes of this section, wearing a  helmet
  means  having  a  helmet  fastened  securely  upon  the  head  using the
  manufacturer's fitting guidelines for the particular model used.
2. Any person who violates the provisions of this section shall pay  a
  civil  fine  not  to  exceed two hundred fifty dollars. A police officer
  shall only issue a summons for a violation of this section by  a  person
  less than eighteen years of age to the parent or guardian of such person
  if  the violation by such person occurs in the presence of such person's
  parent or guardian and where such parent or guardian is  eighteen  years
  of  age  or  more.  Such  summons shall only be issued to such parent or
  guardian, and shall not be issued to the person less than eighteen years
  of age.
3. (a) The court shall waive any civil fine for  which  a  person  who
  violates  the  provisions of this section would be liable if such person
  supplies the court with proof that between the date of violation and the
  appearance date for such violation such person  purchased  or  rented  a
  helmet.
(b) The court may waive any civil fine for which a person who violates
  the  provisions  of  the section would be liable if the court finds that
  due to reasons of economic hardship such person was unable to purchase a
  helmet.
4. The failure of any person to comply with  the  provisions  of  this
  section  shall  not  constitute contributory negligence or assumption of
  risk, and shall not in any way bar, preclude or foreclose an action  for
  personal injury or wrongful death by or on behalf of such person, nor in
  any way diminish or reduce the damages recoverable in any such action.