Websites
College Splits
GMAT Hacks
Tennis Abstract
Heavy Topspin
GitHub

In 2006, he and Kent Bonham founded College Splits, the primary provider of collegiate baseball data for MLB clubs.

Jeff has written several GMAT textbooks: Total GMAT Math [PDF | print], Total GMAT Verbal [PDF | print], GMAT 111 [PDF | Kindle | print], and a set of 1,800 practice GMAT math problems [PDFs]. Jeff has worked with several major GMAT-prep companies to develop and improve their student resources.

Jeff also spends a lot of time thinking about tennis. He created and maintains the online encyclopedia Tennis Abstract and publishes tennis research at Heavy Topspin. He was a regular contributor to The Economist's Game Theory blog, and his work has also appeared at FiveThirtyEight, Tennis Magazine, The Wall Street Journal, and ESPN.com.

In 2015, he spoke about tennis analytics at the Sloan Sports Analytics Conference and subsequently published an extensive database of tennis results, rankings, and stats. He founded and maintains the Match Charting Project, which is relied upon by everyone from broadcasters to the coaching staff of Iga Swiatek. It could always use your help.

In 2022, Jeff published The Tennis 128, a 300,000-word series of biographical essays counting down the 128 best players of the last century. The following year, he celebrated the 50th anniversary of 1973, one of the most consequential seasons in the sport's history.

A long time ago, Jeff was a professional saxophonist and bandleader. He performed with a variety of groups, including his own Oy Christina! jazz orchestra and with James Brown's original "funky drummer," the late Clyde Stubblefield. Four of his albums are available on Bandcamp, including two with his 15-piece jazz orchestra.

Han bor i Oslo og snakker veldig dårlig norsk.