Not yet 23, the New York Islanders' Dennis Potvin was already ""some kind of hockey player,"" as they say on the illiterate airwaves. Rookie of the year in 1973-74, next time around he led his three-year-old expansion team to within one game of winning the 1974-75 Stanley Cup. And, next time around he made the NHL's first All-Star Team, and succeeded hockey's premier player, Bobby Orr (injured much of that season), as the league's top defenseman. He became only the second NHL defenseman (Orr was the other) to score 30 goals in a season. What else could one ask of this hockey wunderkind? Well, not false modesty, certainly, because Potvin has always been supremely confident of his athletic prowess (he weighed 185 at age 14), and he still wonders if he shouldn't have played football. He is determined that the business of being a top pro athlete will be parlayed into a highly profitable career off the ice. He reminds us that he is no mere jock--he reads, he goes to art galleries, he enjoys New York (unlike most of his Canadian buddies). His single-mindedness would grate if he weren't so bloody candid about the harsh requirements and ugly fury of his chosen sport: ""There was a consummate feeling of satisfaction over having delivered the perfect bodycheck--under the circumstances--and a terrible feeling of guilt over having pulverized someone I didn't even know."" Despite the obligatory hockey book padding (e.g., his own personal All-Star line-up), his story has the relentless energy and fierce drive of a well-executed power play.