It's obvious to any fair minded fan that Strauss was not trying to do a tip tackle.....so what happened? Well Wikus checked and hopped. Strauss took him as his weight was transferring up and drove.
The physics of that are obvious. The tackler pushing forward tends to push up......the legs are the point of contact, so they go up.....and the unsupported upper body goes down. I think much the same thing happened with the Welsh skipper at the RWC. These things are matter of physics, more than intention and they happen in a blink of an eye. That's why the red against Wales was so out of proportion.
Parenthetically in the NFL you see wide receivers taking these falls all the time......these guys learn how to bridge with one arm while still retaining possession with the other.


