By Blake Brittain

March 23 (Reuters) - The National Collegiate Athletic Association has sued sports-betting giant DraftKings DKNG.O over its marketing for online gambling on the famed U.S. college basketball tournament known as "March Madness," citing risks to NCAA athletes and the group's reputation.

The NCAA's lawsuit, filed on Friday in federal court in Indiana, seeks to bar DraftKings from using trademarked phrases for the tournament including "March Madness," "Final Four," "Elite Eight" and "Sweet Sixteen."

The college sports association said in the lawsuit that it has refused to partner with gambling sites because of a "strongly held belief that sports betting jeopardizes competitive integrity, endangers student‑athletes, and invites manipulation of games."

The tournament, which determines the U.S. men's and women's collegiate national basketball champions, started last week. The gambling industry trade group American Gaming Association estimated that Americans would bet $3.3 billion on March Madness games this year.

The NCAA said DraftKings began misusing its trademarks on the betting site "on the eve of the tournaments," falsely associating the group with the site and tarnishing its reputation.

A DraftKings spokesperson said the company "does not use the term March Madness as a trademark," but uses it and related phrases to "accurately identify" the basketball games in a way that is protected by the U.S. Constitution.

Spokespeople and attorneys for the NCAA did not immediately respond to requests for comment on the lawsuit on Monday.

The lawsuit said DraftKings' "prop" bets, in which gamblers bet on individual players hitting specific milestones, are particularly harmful because they "increase exposure to harassment and pressure from bettors, and create incentives for improper influence."

NCAA president Michael Selig has separately asked the U.S. Commodity Futures Trading Commission to suspend college sports prediction markets on sites like Kalshi and Polymarket until there are stronger safeguards around them. Selig told the CFTC that the association has also "consistently advocated for the elimination of college sport proposition betting markets."

Friday's lawsuit seeks an unspecified amount of monetary damages as well as an order blocking DraftKings' alleged trademark infringement.

The case is National Collegiate Athletic Association v. DraftKings Inc, U.S. District Court for the Southern District of Indiana, No. 1:26-cv-557.

For the NCAA: Lee Marshall and Matt Minder of Bryan Cave Leighton Paisner; Ryan Hurley of Faegre Drinker Biddle & Reath

For DraftKings: not yet available

(Reporting by Blake Brittain in Washington)