Final answer:
Jon and his friends' frontward somersaults down a hill is a motion called roll, which is a rotation around their longitudinal axis. Other motions like pitch and yaw involve different axes of rotation, and options Hay and Raw are not standard motion terms.
Step-by-step explanation:
When Jon and his friends are doing frontward somersaults down the grass hill during Blue and White Weekend, they are exhibiting the motion known as roll.
Roll refers to the type of motion where an object rotates around its longitudinal axis, which is an imaginary line running from the head to the feet when considering the human body's orientation. This is similar to the motion observed when a log rolls down a hill; it continuously rotates around its central, longitudinal axis as it moves down the slope.
The other options provided in the question relate to different types of motion: Pitch is rotation around the lateral or transverse axis, like a person jumping on a trampoline and leaning forward or backward while in the air. Yaw refers to rotation around the vertical axis, analogous to a rocket blasting off from Earth and turning left or right without rolling or pitching. The options Hay and Raw are likely meant as distractors and do not correspond to the standard terminologies for describing motion in physics.