Emmanuel Sanders taken out with violent hit, but was it illegal?

You're never going to remove the violence from the NFL. The league wants the game to be safer, and that's necessary, but sometimes brutal hits are going to happen.

Receiver Emmanuel Sanders took one on Sunday in the St. Louis' Rams 22-7 upset of the Denver Broncos.  

Sanders was going for a catch along the sideline in the third quarter, and was hit hard by St. Louis Rams safety Rodney McLeod. It was a violent, rough hit that left Sanders on the ground for a while. McLeod got a penalty for the hit, and that's where the debate comes in.

McLeod looked like he led with his shoulder and hit Sanders in the shoulder. If there was helmet-to-helmet contact, it was just the physics of two professional athletes going full speed into each other.

Was that illegal? Sanders walked back to the locker room after the hit (joining tight end Julius Thomas, who was ruled out with an injury, on the sideline) and it looked incredibly painful. That doesn't make it illegal, however. What else was McLeod supposed to do?