If anyone still doubts that football is a violent, unforgiving game, Karras will set him straight. A born exhibitionist, Karras these days shares the spotlight with Howard Cosell on ABC's ""Monday Night Football""--and he's assumed some of Cosell's swagger and truculence here. Not so many years ago, Karras, the son of Greek immigrants, could be found in the starting line-up of the Detroit Lions and pummeling all comers, on and off the field. He even took on NFL Commissioner Pete Rozelle when the latter suspended him in 1963 for gambling and associating with undesirable elements in the Detroit bars. ""I wasn't a nice guy,"" says Karras, who admits to ending a rival's career on the Iowa Hawkeyes when he ripped the guy's knee ligaments. His bravado put him at loggerheads with coaches and management (""I hate whistles. . . because they're symbols of authority and subservience"") throughout his playing career--when he wasn't playing football, he was wrestling as ""Killer Karras"" to pick up extra cash. How about the tender tough-guy title? That's mostly for his childhood in Gary, Indiana, where his saintly father died while Alex was in high school, and maybe for the pain of seeing his elder brother suffer a nervous breakdown trying to cope with the pressures of the NFL. A bruised ego is frequently evident here, but otherwise sadness is mostly transformed to anger in this cocky little book that plays up the not-so-nice side of the sport.