How much force is OK when a fan gets loose on the field?

articles.baltimoresun.com — This is not about disrupting or interfering with a baseball game. It is about security. No one knows what will happen next when a fan gets loose in a packed stadium; there isn't time to stop and think, 'Oh, it's just a teenager.' He or she has to be corralled, and if Tasering shortens the process, do it. May 25, 2010 View in Crawl 4

How much force is OK when a fan gets loose on the field?