Like Blake said, I think this might be a flexibility issue. Look into his suggestions; those Snatch and Clean Deadlifts -- especially segment pulls -- are going to help you out.
If this isn't a result of the aforementioned issue, I'm going to offer up another suggestion that's slightly different: widening your feet in the start position, especially in the snatch. Based on people's limb lengths and comfort in the set up, I sometimes recommend that certain lifters spread their feet out during the set up. This seems to alleviate some issues, one of which is the shin scraping.
If it isn't any of the above, then it could be a result of inconsistency in your start position. If you're relatively new and doing a dynamic start, then you might want to revert back to a static start, or slow down the dynamic start, in order to build consistency.
You want that bar to have room to go back, but be careful to not put the bar too far away. The bar should generally be positioned over the mid-foot area to start out; if you're too far away, then your balance is going to be really out of whack.
Hope this helps,
Javier A. Sanjuan
Olympus Barbell Club
Dear God, please help me lift heavy and be awesome. Thanks. Amen.