You know what he could have done? Led with his hands/arms. Cocking your shoulder to pop a guy that's sliding is dumb as hell. I'll be surprised if he's not fined.
Personally, that's the rule change I would make. Every tackle has to be hands first. It'd change the game, but it'd cut way back on brain injuries.
I didn't see the replay. But did the Redskins defender mean to make contact in the receiver's body and misjudged the momentum of both players ?