By definition, a shank results when your hands are closer to the ball at impact than they were at address. Let's look at the most common causes...

1. Lunging at the ball. When we lunge, our weight goes onto our toes rather than remaining on the balls of our feet. This moves our body (and hands) closer to the ball increasing the chance of hitting on the hosel. Many times the player committing this error exacerbates it by moving away from the ball thinking he/she is standing too close when it is usually the opposite. Moving away increases the lunge and makes the problem worse, not better.
2. Tight grip. Combine a tight grip with #1 and you have the perfect recipe for a shank. When we tighten our grip, arms do not swing properly leaving the clubface open and the hosel leads into the ball.
3. Usually when shanking a pitch/chip, #1 and #2 do not apply. A chip/pitch that is shanked is usually due to a very loose, "armsy" stroke with not a lot of club control.

There are definitely other ways to hit the hosel but the ones listed above are the most common.