A sandicap is a sandbaggers handicap. In golf, one plays to their specific handicap, which allows them x shots per round. However, some take advantage of this and claim they are worse than they actually are in order to gain more strokes. This type of person would be known as a sandicapper.
Even though Dan usually shoots par for the course, he has his handicap listed as a 10. This 10 would be Dan's sandicap.