It is illegal to stream copyrighted material like NFL games, etc. However it is not illegal to watch them and nobody is chasing the end users.
Most of the sites streaming the games are international however and are not subject to U.S. law. They are typically linked to Reddit accounts with multiple IP's through VPN's. They make their money by having auto links sending a user trying to access the stream to three or more websites that pay the streaming service for the clicks. A good browser security package prevents any harmful malware viruses or trojan horses since it is not profitable to eliminate customers that make them money.
