Zimmerman graduated from Horace Mann School in the Bronx before becoming a college football player at Stanford and Columbia University, where he wrote for the Columbia Daily Spectator. An offensive lineman, he was a member of a United States Army football team while stationed in Germany, and was later a four-year player in New Jersey semi-professional football leagues. Zimmerman began his formal journalism career at the New York Journal-American and the New York World-Telegram and Sun before moving on to become a regular at the New York Post in 1966. In addition to football, Zimmerman covered three Olympic Games for the Post, including the hostage crisis at the 1972 Summer Games in Munich, Germany.
Zimmerman also wrote a regular wine column for the Post, and his wine opinions are often referenced in his weekly mailbag, with football fans adding wine queries to their football questions or comments.
In 1979 Zimmerman moved to Sports Illustrated, where he writes a weekly column and game predictions, and awards the magazine's yearly All-Pros. These days, Zimmerman is best known for NFL picks that are published every week during the NFL season. He is notorious for hedging his bets. For instance, he'll pick the Cowboys--as long as they can stop the run.
Since the mid-1990s, Zimmerman has been a frequent contributor to Sports Illustrated's website. Zimmerman provides the site with a weekly column - "Power Rankings" - of his estimations of the relative strengths of each NFL team, as well as a reader mailbag feature, in addition to his other contributions to the magazine.
Zimmerman's method of football analysis is a comprehensive one. His charts include both subjective opinions on the players and gameplay as well as objective statistical information. At any point afterward, he can then give detailed analysis of the players, teams, and games that he charted, tracking who plays well against whom, which players are improving or declining, which superstars are over-hyped, and which underrated players to "plug" in his writings.
Zimmerman also writes a weekly on-line mailbag. He writes in a stream of consciousness style rather than a simple question-and-answer, liberally sprinkling in tidbits of football history, pieces of popular culture, quotations, admittedly bad jokes and puns, rants, and wine advice. He also frequently attributes a running commentary to his wife Linda, a.k.a. the "Flaming Redhead."
Annually, Zimmerman rates the performance of television NFL sportscasters, criticizing those announcers who do little more than hype the stars while making inane comments on the game, ignoring the strategy or play of the game, or generally making mistakes in their commentaries. Zimmerman also goes out of his way to praise the sportscasters who provide meaningful, intelligent commentary for football fans.
While covering the NFL draft for ESPN in the '80s, Zimmerman was asked what the NFL player of the '90s would be like. Zimmerman responded, controversially, "The player of the '90s will be so sophisticated that he'll be able to pass any steroid test they come up with," ending his television career. He has recently appeared in video features on the SI website with swimwear model Brooklyn Decker.
In January 2008, Zimmerman correctly predicted that the New York Giants (an overwhelming underdog) will win Super Bowl XLII over the New England Patriots.
Zimmerman's style shows similarities to New Journalism, and this influence is especially evident in his web entries. Zimmerman named Jimmy Cannon as one of the sports writers he most admires. Zimmerman described George Orwell as his "literary idol," and his writing shows some thematic similarities with that of the late novelist. In the 1980s, Zimmerman, a self-described "round-head", was the last writer at Sports Illustrated allowed to persist in using a typewriter and fax to file his stories when all the rest of the writers had started using computers.
Zimmerman is the author of the football tome The Thinking Man's Guide to Pro Football (Dutton; revised edition, 1970) and his 1984 update of that book, The New Thinking Man's Guide to Pro Football (Simon and Schuster). His other books include Football Lingo (WW Norton 1967, with Zander Hollander); The Linebackers (a 1972 short text for Scholastic Press); The Last Season of Weeb Ewbank (Farrar Straus and Giroux 1974); and Duane Thomas and the Fall of America's Team (Warner Books 1988; credited to Thomas and Zimmerman, it contains diary entries by Thomas but otherwise the text is that of Zimmerman). He currently serves on the 44-member Pro Football Hall of Fame selection committee, and formerly was a member of the Hall's smaller Senior Committee, a position which Zimmerman resigned in protest over the committee's repeated rejection of players he deemed worthy candidates.