Football rule differences NFHS vs NCAA
 

What would be your top 5

Also top 5 penalty enforcement differences.

5 Key Rule Differences
A player in the neutral zone is offsides and a live ball foul
There is more latitude on low blocks although they are still legal by default
KCI has a 1-yard semi-halo
Passer can legally throw ball away if outside tackle box and pass beyond LOS
4th down fumble rule and forward fumble out of bounds

5 Penalty Enforcement Differences
DPI is a spot foul inside 15 and an exception to half the distance
Live ball fouls by A on kicking plays can be tacked on to the end of the return
Runs that end behind the LOS have a basic spot of the previous spot
Fouls by A behind the LOS are enforced from the previous spot
DPI, UNS, and PF are automatic first downs