There are two main rule changes this year that apply to high school football. Veteran official Jeff Shinn has submitted the following explanations, as well as an explanation of the the rule regarding tripping:

Horse Collar Tackle

Rule # 9-4-3.k states “No player or non-player shall grab the inside back or side collar of the shoulder pads or jersey of the runner and subsequently pull the runner to the ground.” That is the definition of a “horse collar tackle”. Merely grabbing the collar is not a foul.

Sideline restrictions

The other main rule change relates to the sideline. Rule #1-2-3g. states “Team boxes shall be marked on each side of the field outside the coaches’ area between the 25-yard lines for use of coaches, substitutes, athletic trainers, etc., affiliated with the team. The coaches area is a minimum of a 2-yard belt between the front of the team box and the sideline, and becomes a restricted area when the ball is live.” Rule #9-8-3 further states “A non-player shall not be outside his team box unless to become a player or to return as a replaced player. A maximum of three coaches may be in the restricted area. No player, non-player or coach shall be in the restricted area when the ball is live.”
Tripping

One issue arose at the Etna v Tulelake game last Friday. An Etna player was running along the sideline in possession of the ball. A Tulelake defender was slightly out of position and stuck a leg out to trip the runner, bringing him down. This is not a foul. Rule 2.45 states “Tripping is the use of the lower leg or foot to obstruct an opponent, who is not the runner, below the knee.” In other words, “tripping” is a foul, unless it is the ball carrier. Then it is not considered tripping. It is considered a tackle.