Clay Matthews, 52 on the Green Bay Packers, is a famous linebacker. He has the all-time sack record for the Packers and has been in many commercials from Old Spice to Play Station. Let us look at some stats:
Weight: 225 lbs (102.06 kg). Top Speed: 20.03 MPH (8.95 m/s)
Imagine you are a quarterback, and Clay Matthews is running at you... You try to get out of the way but you simply cannot... all of a sudden... BOOM, you just got rekt because Clay Matthews sacked the snot out of you. How much force did you get hit with? Let's look.
p=mv -> p=(102.06 kg)(8.95 m/s) -> p= 913.44 N*s.
Clay Matthews, at top speed, has a momentum of 913.44 N*s. Now, let us suppose that from the first point of contact to the point that Clay Matthews has fully hit you, arms wrapped around you and everything, is about 0.15 seconds.
(913.44 N*s)/(0.15 s) = 6089.6 N... Newtons -> Pounds = (6089.6)(0.224809) = 1368.99 pounds of force.