The jock in question, seventeen-year-old David Green, captained his Connecticut prep school football team through a luckless (1-6-1) but dedicated 1973 season--to the intense surprise, anxiety, and vicarious elation of his weak-ankled, overweight father. Green pere slogs relentlessly yard by yard through every glorious, ignominious, heartbreaking game, with many a strenuous meditation on his own sorry athletic record (""Reason with them,"" said Gerald's mother of the neighborhood toughs; he didn't learn to ride a bike until the age of twenty-two) and the dream-fulfillment of it all (""My son has made me an American"" and ""I'm one up on Mailer,"" some unconquerably irrational part of his mind exults). The portrait of David is deft and affectionate: in a family of eggheads he is an anomalous throwback to some fiery, persevering, and unabashedly physical Sicilian ancestor. Less effective are the standard ruminations on The American Winning Mentality (Vince Lombardi, Nixon, Watergate), and the klutzy-father-vs.-can-do-son theme is sometimes moving, more often a thin cliche. Slight but intermittently appealing.