"Red7 tackles blue player, 7 gets up legally, grabs ball, then is quickly wrapped up by supporting blue players.Ball unplayable, who gets put in ? "
Taff, I think you're right. No mention in the OP of Red 7 being taken to ground. The missing piece is another Red player joining to create the maul. If the ball is not on the ground (ruck with ball unplayable, Red put-in) and no maul has formed (no second red) but the ball is unplayable (not sure how as Blue can still execute a tackle) then my guess is 'team going forward'.