premise: Boys and men, mostly all wearing helmets, hang on to two separate cars while they ride skateboards. hypothesis: Boys and men are playing baseball.
contradiction: You cannot play baseball and skateboard at the sametime because baseball is played in a field and skateboards will not roll on grass. Cars cannot be driven in a baseball field. In baseball only the batters and backstop will wear helmets so only just over half of the players will be wearing helmets which is less than mostly.