To be fair to Rioli, we don't know what he was going to do. Yes, he was slinging Keane to one side, but then SPP poleaxed Keane and basically knocked both players to the ground.There is no doubt SPP lined him up for the bump.
But the bump was made more severe with Rioli's sling tackle.
If SPP didn't bump Keane, Rioli would be looking at 3 to 4 weeks.
And yet, no free kick for either action.
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It does seem likely Rioli was trying to bring Keane to ground, and yes, that may have resulted in a sling tackle. Given Keane is a much taller player, it was foolhardy of Rioli to try to bring him to ground that way, because it certainly did risk being a sling tackle.
I've always said - best tackle technique is to wrap your arms around the player and drop your knees - try to bring him straight down. I think some players go the sling because they don't want to allow the other player - if they're strong enough - to stand in the tackle. But too bad, I guess; if the other player is a Crouch or Dangerfield, you don't get to negate their strength by slinging them.