Fantasy arena combat game by Reiner Knizia. Published by Avalon Hill 1997. 3-6 players.
Titan: the Arena is a rework of Reiner Knizias "Grand National Derby".
A sci-fi themed rework by Don Greenwood is called "Galaxy: The Dark Ages". This one is published by GMT Games year 2000.
You bet on different creature cards and play strength cards on them later to make your bets win in the combat phase.