Coach Harris is correct. Also, I don't know if there was ever a "rule" about the knee hitting first, but if it was, it was many, many years ago. Like so many calls in wrestling, there are numerous variables and situations involved that laying down and black and white guidelines will end up just making it more confusing. Most experienced officials know it when they see it. The over-riding principle is you are responsible for returning your opponent to the mat safely.
It doesn't have to be an intentional act. You can lose your grip and drop your opponent on a lift and that can result in the call. If you whip your opponent down from a kneeling position (not standing)with an arm trapped and if he's unprotected and hits the mat with force it can result in the call. This one is sometimes a harder call because there might not be a lot of elevation but the momentum is there and the head ends up richocetting off the mat and that's got to hurt.
Going to the mat from your feet and "pile driving" into your opponent with a shoulder is an easy call and called quite often. And the classic bear-hug with a power-driver finish is similar and easy to call. Sometimes the heavier kids go the mat hard...but they have there own weight behind them and that can't be avoided...when you are nearly 200 pounds or more it is "necessarily" going to be a rough landing....
But there's a whole lot of situations where the official just doesn't think it was unnecesary force. Sometimes a kid's hands, arms, or legs will hit and make a big slapping noise but there is really no force behind the move, but it sounds like it.
