What creates a shank? To put it simple it is when the sweet spot gets too far past the ball line or target line. This can be done a few ways. One is a club that gets too steep on the downswing, works outside the ball line, and cuts sharply across. Another is more of a better player problem when the sweet spot comes from too far in to out and the sweet spot is working across the ball line too much. Where a third option is having a good swing direction but the sweet spot is just too far away from the player resulting in a hosel strike.
Lets take a look at the first scenario where the club gets outside the ball line too early and works across. This is what we see most often and comes form a player that has a club traveling too steep and an open club face on the way down. The player is trying to square up an open face or get a playable ball flight by swinging left. This way the face that is open to the path that produces slices will start the ball left of the target and move into play somewhere. The featured image above shows a club head in blue that is outside the ball line 1′ away from impact. If that club head does not move quickly left to find the club face or toe of the club there is the hosel waiting for some action.
Typically, but not all the time, players that pull their club inside too fast and open the face on takeaway get the club into a positions at lead arm parallel that is too shallow. From there in order to get the club head on the ball and the face closed they move the club head form the top out into the ball. This gets us into a position that the player has limited options to hit a functional shot. Below is a screen shot of a club going back too far to the inside and open (left) and coming down too far out in front of the grip (right). Click on the image for the 1 minute YouTube clip on this pattern.
Now let’s take a look at a good player that does the opposite. They take the club back more around the hands, this guy takes it slightly outside, and the club face is looking more towards the ball. The club head has not been rolled behind and open. If they were hitting a chip shot it would be easy to get the club back on the ball from this position without a lot of manipulation. On the down swing (right) the club head is coming down slightly behind the hands and you can see it is further away form the ball line and more toe down. From here the club can enter into the ball on more of a shallow angle closer to the white line than steeper on the yellow line. Click the image for a 1 minute YouTube clip on how this club comes into the target line, collects a ball, and leaves the ball line.
To see the difference of the in and over (blue club) and up and back (yellow club) click this image for a 1 minute video comparison. 
