It’s contracts - assuming they will remain active throughout the events - but are live now.
All based on winner to receive $1.00 per contract (100 per transaction) and limit orders just like securities.
Looked at it a little earlier today - some good values on heavy ML faves - able to bid on something like St John’s in their first round matchup at 96 cents I think.
Some of the markets are chalkier than the books it felt like - especially women’s tourney.