What is one rules for blocking in the NFL?

Answer 1

There are two halves in footy matches (45min each) unless it goes to extra time.

another rule is if you foul a person, you get yellow or red cards according to the strength of the foul.

Answer 2

There are a lot of rules and definitions for blocking, depending on the player who is blocking, whether it is in the free blocking zone, whether the player is on the line of scrimmage or not, whether the player is on offense or defense.

The NFL rules are not publicly available, so getting specific answers may be difficult. I can give you NCAA rules, but I need a more specific answer so I don't have to type 8 pages on the various blocking rules for various positions, etc...