Hey-three decades have passed since the 65-year-old Bob Cousy retired after leading the Boston Celtics to six National Basketball Association championships between 1957 and 1963. So when the Hall of Famer-turned-actor was asked to shoot free throws for a scene in Blue Chips, he did something that shocked the film's cast and crew: He nailed 21 in a row. ''That's not a big deal,'' insists the bespectacled, gray-haired ''Cooz.'' But then it was time to shoot the same scene from a different angle-and Cousy was forced to wait in his air-conditioned trailer on the film's Indiana set for an hour and a half. ''I had been loose as a goose because it was such a hot day,'' says the voluble Cousy, now a television commentator for the Celtics. ''Then my muscles tightened up, and I couldn't make two in a row. (Director) William Friedkin was looking at me like, 'What's going on here?' And Nick (Nolte) was laughing his buns off.'' But the theme of the new film-the buying and selling of ''blue chip'' high school players-is no laughing matter to Cousy, who signed on to play the athletic director of fictional Western University because he felt Blue Chips realistically portrayed the corruption that pervades college basketball. Having known plenty of coaches and their programs-he guided Boston College for four years in the '60s-he has seen the phenomenon up close. ''It's like crime in the streets,'' the straight-shooting Cousy declares. ''You can't control it, you can't have a cop on every corner. The NCAA has 700 schools and maybe a dozen investigators. It's worth literally millions and millions of dollars to a college to get someone like (Chips costar) Shaquille O'Neal to come to their school. And as the pot grows, the amount of cheating grows commensurately.'' While endorsement-monger O'Neal-who also released a rap album, Shaq Diesel, last fall-seems likely to continue branching out into movies, Cousy says he can't abide the hurry-up-and-wait reality of filmmaking. ''This is my maiden voyage and my swan song,'' swears Cousy, who shot six scenes in 26 days with Nolte, though only three survived Friedkin's final cut to make it into the finished film. ''The 80 percent of the time I spent in my trailer is the closest I've ever come to having a nervous breakdown. I remember saying to Nick, 'God! No wonder everyone in Hollywood is so screwed up!'''