The first known sit in was done in Greensboro, North Carolina, 1960 by 4 african american males, Ezell Blair Jr., David Richmond, Franklin McCain and Joseph McNeil. Sit ins were known to be very harsh. The protesters would be thrown food and would be beaten up to the point were they couldn't take anymore.
The protesters will usually simulate the whole sit in before they go, by means of hitting and yelling at each other trying to make the simulation as realistic as possible. They had to know how it felt like to be able to stay strong throughout the protest.
*Remember the point of a sit it is to not fight back.