I have always enjoyed visiting with parents who arrive 10 or 15 minutes early to pick up their kids from practice and I have no complaints about a parent watching an entire practice from a distance so long as they are only watching and not communicating with their kid. Much more than that can disturb practice and I think should be avoided.
The bigger problem is the dad who sits 160 feet down the foul line telling his outfielder DD where she should position herself, oftentimes contrary to what the coaches are telling her to do.
