A baseball feild is a large area for 4 or 5 security guards (who are often out of shape, etc) to patrol and keep people from running around. People know the rules. I say fair game. By the age of 12, concrete reasoning skills are instilled in adolescents. Unless they are retarded, they are fair game. They know the rules. As someone said, "play stupid games, win stupid prizes." That's rough about your brother, good thing he was never tazed. Cops are not held responsible for an individuals personal health however. They do not have the advantage of knowing whether someone has a heart condition of not... Once again, the audience should know not to jump on the field.
A) He was shot by LEO, not security.
B) The poor physical shape of the officer in question is not a valid excuse.
C) Yes, you're right, cops cannot be expected to know the conditions of the people they encounter, and in case where the cop or other people are in danger, of course, go ahead and use the taser, but this kid was just being an idiot. who was he going to hurt even if he ran around for another 10 minutes?

He was being stupid. Not dangerous. And in my opinion, that does not warrant the use of less-lethal force.

We've delt with crazed sports fans for PLENTY of years without using tasers.