Um...what I do on my lunch break is none of the boss' business unless I am doing something illegal or unethical.  This boss sounds like a micromanaging, short-sighted, control-freak.  Firing someone for what they do on their lunch break, on their own equipment, is possibly illegal and definitely unwise.  Demand they don't play on premises, sure, but once I clock out for lunch and leave the area, there are few things that are less of the company's business.  God forbid that your employees get some exercise while doing something they enjoy.