Parents experience anxiety while they are on the sidelines as well. Each sport creates its own level of anxiety in parents. It may depend on the level of contact in the sport or the skill level of the participants, but most parents start living the game with their child. They can see themselves out there on the field and they can feel the muscles twitch in their body as they feel their child catch a pass and then fumble. Or they feel the elation when their child hits a home run.
Most parents live through their children to some extent while the child is on the athletic field.
Unfortunately, parents do not have the same outlet for the release of building intensity that players do during a game. Parents can't block the opponent. They can't dribble the basketball and focus their anxiety on that activity. They literally lose sight of what is important in youth sports. Tunnel vision is often the reason parents act out at the game.