I assume you are asking a ball game language. Say for example, when you play basketball, you must hit the ball on the ground when you walk, but 走步 meant you did not hit the ball on the ground when you walk more than 1 step. This will break the rule and be punished if so.
For double, it normally meants the same person hit the ball twice, say for example, the volleyball. This will also break the rule and be punished.