It's the same thing happening again and again. Batsmen are playing for the turn and the odd ball is straightening. Leach bowled this on a good length, Rahane wen't on the backfoot, looking to cut it behind point, the ball straightens and hits his back leg before the bat and he knew it was plumb so he just started to take the long walk to the pavilion.
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Watch Rahane's dismissal here: