Broken balance wheel

More likely a broken balance staff. The axle of the wheel as it wee. These used to break quite regularly before shock proofing. As for fixing it, this depends on who made your pocketwatch and how common the movement is. Most were made in large enough numbers and like I say it was a common break in the past, so old stock balance staffs are usually easy enough to find on ebay and the like(or a full working movement you can take parts from). Then the cost of a watchmaker fitting it and doing general service. I'd reckon 3-500. If you can put pics up, especially of the movement that would help narrow it down.