Soft Book
In short: A sportsbook that prices markets to attract recreational action rather than match sharp consensus, charges higher vig, and limits or bans customers who show sustained edge. Most major US retail sportsbooks operate as soft books.
Also known as: square book, recreational book
A soft book’s business model depends on recreational bettors who place bets on perceived favorites, parlays, and home teams — and on quietly removing customers who beat the closing line. Vig is typically 4–6% on standard markets versus 2–3% at sharp books, and lines often move based on betting volume rather than sharp action. For arbitrage and +EV bettors, soft books are where most of the opportunity lives, but the same business model that creates the edge is also why account limiting is so common there. DraftKings, FanDuel, BetMGM, and Caesars are the largest soft books in the US market.