On question 1, How? You say, Coach, you are fired.
On question 2, Why? Depends on perhaps 25,000 to 1 million variables. For example, if the Coach smoked Crack Cocaine with the kids. That's something that can get you fired. If the Coach openly worshiped the Devil and encouraged players to sacrifice animals. That can get you fired. If the Coach committed murder, then this could get the Coach fired. If the Coach had not won a game in 6 years as Coach, that could get him fired. If the Coach was a racist, that could get him fired. If the Coach developed a strong liking for drinking human blood, this could also be concerning. I've listed a few out of the potential 1 million scenarios. Hopefully this answers your questions.