In kickball, kicking does not only mean that a player's leg and foot make contact with the kickball. In order to successfully get a hit, the kickball must land in fair territory and the kicker must safely reach base. There are many different ways a kicker attempts to hit the kickball:
A clean hit is a kickball that lands in fair territory without having been touched by a fielder. It commonly refers to a kickball that travels through the infield without being touched by an infielder, or a kickball that goes over an outfielder's head.
A line drive is a hard-kicked kickball that travels through the air, but relatively low/close to the ground without touching it. Line drives can be hard to field unless hit in a fielder's direction, and have a fairly high tendency to become successful hits.