I heard plenty about this tackle all afternoon, but first impressions after seeing the video I felt it really wasn't all that bad. Broad does exactly what every player does when tackling an opponent - went hard to wrap him up & took him to ground to force a stoppage. It was actually a first class tackle. There was no high contact at all, his head hitting the ground caused the concussion, but it was more unlucky than careless.
I dunno, but I've seen plenty worse than this not even get looked at ...
In the classic (illegal) sling tackle the tackler goes to the ground first, then pulls his man down & slings him across his body. Tremendous leverage & centrifugal force can be generated by the slinging action, but Broad did nothing like that. Broad had both arms around his man all the way to the ground, there was no significant slinging action.