I presume, not being much of a bowler, that the reason he does better to lefties is because of the amount of spin? An arm ball,bit of drift maybe and goes straight on,lefties play for spin, through the gate and bowled.
For right handers, the only real way would be for an edge? Much smaller target to hit.
Yeah, that's probably right.
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I don't know much about spin bowling either, (Wish I brought my Bob Woolmer book with me now!) but I know from bowling it that off spin bowling from round the wicket is pretty different from over. Maybe because of the way your body works as a whole, as you twist a little more when bowling from round the wicket, so maybe more revs and drift. Also, you play deliveries moving into you differently from deliveries moving away, so good right handers have no problem playing balls that move into their pads. A coach once told me that I should look to bowl outswing rather than stick with my inswing, because as I go up a few levels, you'll find that batsmen prefer to play in-swing, as they just let the ball run off the bat, but as soon as you get that lateral movement away from them, that's when you will get an edge. After you bowl a few overs of that, and the batsmen get used to that, then bowl the ball that swings in, and pin them lbw or bowl them. As a result, I've not taken many wickets this season…
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I'm guessing in a way, that's basically what Swann is aiming for when he bowls that arm ball to a leftie.