Letter Boxing

From BoardGameGeek:

Letter Boxing is a word game featuring a 72-card deck of single- and double-letter cards. Players take turns placing new cards into a line in the middle of the table, and a player may fold (if they can't go on) or challenge (if they think the opponent can't complete a word). It's a fast game with a mix of word play and risk management. A risky bluff at the right time could earn a huge reward!