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So users who come to thier site from adwords ads and search engines has to close the entire browser to get back to the previous page (search engine,etc).
Is this an adwords TOS violation?
However, consider these other possible issues:
If you got to your competitor's site by clicking on their SERP results, and not a sponsored ad link, they can do whatever they want, and are not bound by G's advertising rules.
If you got there by actually clicking on one of their ad links, you may be guilty of click fraud.
If you typed in their Ad's main displayed URL in your browser's address bar, it may not be, and probably is not, the complete landing page URL specified in the ad.